UNIVERSITY    OF    CALIFORNIA 

COLLEGE    OF    AGRICULTURE 
AGRICULTURAL   EXPERIMENT  STATION 

CIRCULAR  No.  250 
July,  1922 

MEASUREMENT  OF  IRRIGATION  WATER  ON  THE  FARM 

BY 

H.  A.  WADS  WORTH 


CONTENTS 

PAGE 

Introduction 2 

Units  of  measurement  and  equivalents 3 

Weirs 4 

Rectangular  weirs 7 

Cipolletti  weirs 9 

90-degree  triangular-notch  weirs 11 

Weir  construction 12 

Submerged  orifices 14 

Submerged  orifices  of  fixed  dimensions 18 

Construction  of  submerged  orifices  of  fixed  dimensions 20 

Computations  if  tables  are  not  available 20 

Adjustable  submerged  orifices 21 

Theory  of  inch  box  measurement 23 

Riverside  box 24 

Anaheim  Union  Water  Company  measuring  box 25 

Santa  Ana  Valley  Irrigation  Company  miner's  inch  box 26 

Azusa  hydrant 27 

Division  boxes 29 

Mechanical  devices  for  measuring  water  volumetrically 31 

Reliance  meter 32 

Dethridge  meter 33 

Other  measuring  devices 34 

Lyman  meter 34 

Sentinel  meter 34 

Venturi  meter 34 

Venturi  flume 35 

Summary 35 

TABLES 

1.  Discharge  table  for  rectangular  weirs , 8 

2.  Discharge  table  for  Cipolletti  weirs 10 

3.  Discharge  table  for  triangular  notch 12 

4.  Weir  board  dimensions 13 

5.  Dimensions  for  weir  boxes 14 

6.  Discharge  table  for  submerged  orifices  of  fixed  dimensions 19 

7.  Dimensions  for  boxes  for  submerged  orifices  of  fixed  dimensions 20 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


INTRODUCTION 

The  aim  of  this  circular  is  to  make  available  in  a  single  publi- 
cation the  tables,  and  in  some  cases  the  formulae,  necessary  for  the 
measurement  of  irrigation  water  under  the  varying  conditions  found 
in  California.  In  order  to  avoid  confusion,  only  those  methods  which 
are  in  common  use  have  been  considered  in  detail. 

Even  with  this  limitation,  it  has  been  necessary  to  include  a 
considerable  number  of  methods  of  measurement.  This  is  due  to 
the  variation  in  conditions  under  which  irrigation  water  is  delivered. 
As  an  example,  in  the  Orland  area  in  the  Sacramento  Valley,  where 
field  ditches  are  built  on  fairly  steep  grades,  small  weirs  are  used 
almost  exclusively  to  measure  irrigation  water  to  the  water  user. 
In  other  areas  where  canal  grades  are  much  flatter  and  where  the 
head  of  water  in  the  canal  is  subject  to  wide  fluctuations,  the  sub- 
merged orifice  is  used  as  a  measuring  device.  In  general  these  ori- 
fices are  so  built  that  the  size  of  the  orifice  can  be  increased  or  de- 
creased as  the  changing  head  demands.  In  Imperial  Valley,  the 
submerged  orifice  has  come  into  general  use,  largely  because  the  water 
from  the  Colorado  River  is  so  heavily  charged  with  silt  that  the  use 
of  weirs  is  unsatisfactory. 

The  measurement  of  water  in  terms  of  the  miner's  inch  is  prac- 
tically universal  in  most  of  the  foothill  and  citrus  orchard  sections 
of  the  state.  In  these  areas,  where  irrigation  water  is  bought  and 
paid  for  on  the  basis  of  the  miner's  inch,  special  devices  are  in  gen- 
eral use  by  which  a  flow  can  be  measured  directly  in  that  unit  with- 
out the  necessity  of  transposing  from  the  more  common  units  of  the 
other  parts  of  the  state.  Where  individual  pumping  plants  are  in 
use  water  is  commonly  measured  in  terms  of  gallons  per  minute. 

The  common  method  of  payment  for  irrigation  water  in  an  area 
has  had  a  great  influence  in  determining  the  method  of  measure- 
ment in  that  area.  In  most  cases  that  method  of  measurement  is 
used  which  can  be  most  readily  changed  into  the  terms  necessary 
for  the  computation  of  the  water  charges. 

In  addition  to  descriptions  of  the  devices  used  with  these  com- 
mon methods  of  measurement,  which  are  familiar  to  most  users  of 
irrigation  water,  descriptions  of  a  few  unusual  devices  have  been 
included,  either  because  of  the  different  theory  involved,  or  because 
the  devices  seem  well  suited  to  a  greater  use  in  California. 


CIRCULAR  250]  MEASUREMENT  OF  IRRIGATION  WATER  3 

The  tables  for  weir  discharge  and  for  flow  through  submerged 
orifices  of  fixed  openings  are  the  most  recent  and  the  most  reliable 
that  are  available.  The  United  States  Reclamation  Service  and  the 
United  States  Department  of  Agriculture,  Division  of  Irrigation  In- 
vestigations, have  willingly  furnished  tables. 


UNITS  OF  WATER  MEASUREMENT   AND  EQUIVALENTS 

Cubic  foot  per  second. — This  unit  represents  an  exact  and  definite 
quantity  of  water,  viz :  the  equivalent  of  a  stream  one  foot  wide  and 
one  foot  deep  flowing  at  the  rate  of  one  foot  per  second. 

24-hour  second  foot. — This  is  one  cubic  foot  per  second,  running 
continuously  throughout  a  24-hour  period.  It  is  equivalent  to  ap- 
proximately two  (exactly  1.9834)  acre-feet. 

Acre-Foot. — This  is  the  equivalent  of  a  body  of  water  one  acre 
in  area  and  one  foot  deep,  or  43,560  cubic  feet.  One  cubic  foot  per 
second,  or  fifty  southern  California  inches,  or  forty  California  statute 
inches,  running  continuously  for  twenty-four  hours  will  supply  ap- 
proximately two  (exactly  1.9834)  acre-feet. 

Acre-Inch. — This  is  one-twelfth  of  one  acre-foot,  or  the  equivalent 
of  a  sheet  of  water  one  acre  in  area  and  one  inch  deep.  It  is  the 
unit  sometimes  used  instead  of  the  acre-foot,  especially  in  express- 
ing quantities  of  less  than  one  acre-foot.  One  cubic  foot  per  second 
running  continuously  for  one  hour  will  supply  approximately  one 
acre-inch. 

Gallon. — As  many  irrigators  receive  their  water  supply  from 
pumps  and  as  pump  manufacturers  usually  estimate  discharges  in 
gallons  per  minute  or  per  second,  this  is  sometimes  a  convenient  unit 
to  use.  One  cubic  foot  is  approximately  equal  to  iy2  gallons  (ex- 
actly 7.4805)  and  one  cubic  foot  per  second  is  approximately  equiva- 
lent to  450  gallons  per  minute  or  7%  gallons  per  second. 

One  thousand  gallons. — This  unit  is  quite  common  in  irrigation 
practice  in  San  Diego  County,  California. 

Inch. — This  is  a  variable  unit  having  different  meanings  in  dif- 
ferent states  and  even  in  different  sections  of  the  same  state.  The 
old  miner's  inch  of  California  was  the  quantity  of  water  flowing 
freely  through  an  opening  one  inch  square,  the  center  of  which  was 
four  inches  below  the  surface  of  the  water  standing  above  the  open- 
ing; it  is  equivalent  to  a  flow  of  nine  gallons  per  minute  or  1/50 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

cubic  foot  per  second.  The  present  statute  inch  of  California  is 
denned  as  a  flow  of  one  and  one-half  cubic  feet  per  minute.  It  is 
measured  through  an  orifice  one  inch  square  under  a  six-inch  pressure 
and  is  equivalent  to  a  flow  of  11%  gallons  per  minute  or  1/40  cubic 
foot  per  second.  While  the  meaning  of  the  inch  varies  with  local  prac- 
tice, it  is  not  a  stream  of  water  one  inch  deep  and  one  inch  wide,  regard- 
less of  pressure.  Where  its  meaning  is  clear,  the  inch  is  a  convenient 
unit  for  measuring  small  streams  up  to,  say  50  to  100  inches,  and  is 
quite  frequently  used  for  such  streams,  particularly  on  many  of  the 
southern  California  systems.  For  larger  streams  its  use  is  generally 
discarded  in  favor  of  the  more  definite  unit,  cubic  foot  per  second. 

24-hour  inch. — This  is  a  very  common  unit,  especially  in  southern 
California,  and  is,  as  its  name  implies,  one  inch  (the  exact  amount 
of  which  varies  with  locality  and  local  custom)  running  for  twenty- 
four  hours.  Variations  of  this  unit  found  on  some  California  irri- 
gation systems  are  the  one-hour  inch  and  the  twelve-hour  inch. 

The  following  table  will  be  found  useful  in  changing  the  ex- 
pression of  a  quantity  of  water  from  one  of  these  units  to  another: 


Southern 

California 

miner's 

inch 

Statute 

miner's 

inch 

Gallons 

per 
minute 

Cubic  feet 

per 

second 

Acre- 
inch 

Acre- 
foot 

1  southern  Cali- 
fornia miner's 
inch  equals.... 

1.25 

9.0 

fco 

1  in  50 
hours 

1  in  600 

hours 

1  Stat,  miner's 
inch  equals.... 

0.80 

11.25 

Ko 

1  in  40 
hours 

1  in  480 

hours 

1     gallon     per 
minute  equals 

tt 

ill.  25 

^450 

1  in  450 
hours 

1  in  5400 
hours 

1  cubic  foot  per 
second  equals 

50 

40 

450 

1  in  1 
hour 

1  in  12 
hours 

WEIES 

A  weir  is  one  of  the  simplest  and  most  accurate  means  of  meas- 
uring irrigation  water  on  the  farm.  The  weir  of  the  irrigation 
farmer  is  simply  a  bulkhead  or  wall  placed  across  a  stream,  with  an 
opening  cut  in  the  top  through  which  the  water  is  allowed  to  pass. 
This  opening  is  commonly  called  the  "weir  notch."  The  depth  of 
the  water  pouring  through  the  weir  notch  is  the  measure  of  the 
amount  of  water  in  the  stream.  By  gauging  this  depth  and  consult- 
ing the  weir  table  for  the  kind  and  length  of  the  weir  notch  used 
the  amount  of  water  passing  over  the  weir  is  obtained. 


Circular  250] 


MEASUREMENT  OF  IRRIGATION  WATER 


In  some  cases  the  weir  bulkhead  is  placed  in  a  short  section  of 
flume,  called  a  weir  box;  in  others  it  is  placed  directly  across  an 
earth  ditch  and  is  independent  of  any  other  structure.  (Fig.  1.)  The 
theory  and  method  of  weir  measurement  remain  the  same  in  either 
case. 

There  are  certain  conditions  which  must  be  observed  before  a 
weir  can  be  used  for  the  accurate  measurement  of  water.    In  general 


Fig.  1.     Rectangular  field  weir  in  use. 


it  may  be  said  that  the  "weir  crest"  or  bottom  of  the  weir  notch 
should  be  short  enough  so  that  the  amount  of  water  to  be  measured 
will  never  give  a  depth  of  less  than  two  inches  over  the  crest,  and 
long  enough  so  that  the  depth  will  never  be  more  than  one-third  of 
the  length  of  the  crest.  Care  should  also  be  taken  to  see  that  the 
weir  crest  is  long  enough  so  that  the  water  can  pour  through  the 
notch  without  having  to  back  up  in  the  channel  to  a  greater  height 
than  can  be  done  with  safety  to  the  ditch  bank.  A  number  of  other 
conditions  are  usually  laid  down  as  necessary  for  the  weir.  The  most 
important  of  these  are  as  follows : 

1.  The  weir  crest  or  bottom  of  the  weir  notch  must  be  absolutely 
level. 


6  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

2.  The  water  passing  over  the  weir  must  have  a  free  "over-fall." 
If  the  water  in  the  ditch  below  the  weir  is  allowed  to  rise  to  such 
a  height  that  this  free  fall  is  not  possible,  the  weir  is  said  to  be  sub- 
merged. Measurements  made  on  a  submerged  weir  are  unreliable 
unless  complicated  corrections  are  introduced. 

3.  The  distance  from  the  crest  of  the  weir  to  the  bottom  of  the 
canal  or  to  the  floor  of  the  weir  box  above  the  weir  crest  need  only 
be  great  enough  to  check  the  velocity  of  water  flowing  in  the  bottom 
of  the  stream,  say  about  0.5  foot  for  small  weirs. 

4.  The  distance  from  the  ends  of  the  weir  crest  to  the  sides  of 
the  weir  box  or  canal  or  ditch  should  be  about  twice  the  depth  of  the 
water  on  the  weir,  or,  say  from  ten  to  twelve  inches  in  the  case  of 
a  weir  with  an  eighteen-inch  crest  measuring  about  two  cubic  feet 
per  second. 

5.  The  bottom  and  sides  of  the  weir  notch  should  have  a  narrow 
edge.  The  use  of  a  galvanized  iron  crest  to  give  such  a  narrow  edge 
is  quite  common  and  very  satisfactory  but  not  necessary.  Sometimes 
thin  pieces  of  strap  iron  are  fastened  on  the  up-stream  side  of  the 
weir  notch.  In  other  cases  the  board  in  which  the  weir  notch  is  cut 
is  merely  beveled  on  the  down-stream  side  to  a  crest  thickness  of 
one-eighth  or  one-quarter  of  an  inch. 

6.  Water  should  not  be  allowed  to  approach  the  weir  with  a  ve- 
locity exceeding  six  inches  per  second.  Also,  it  should  flow  to  the 
weir  in  a  smooth  stream  free  from  eddies  or  swirls.  Both  of  these 
conditions  are  most  easily  met  by  placing  the  weir  in  a  straight  sec- 
tion of  the  ditch  and,  when  necessary,  by  placing  baffle  boards  across 
the  channel. 

7.  The  depth  of  water  on  the  weir  crest  must  be  measured  suffi- 
ciently above  the  weir  to  be  free  from  the  downward  curve  of  the 
water  as  it  passes  over  the  weir.  For  convenience  in  making  this 
measurement  of  depth  a  stake  with  its  top  level  with  the  crest  of 
the  weir  is  usually  set  at  one  side  of  the  ditch  two  or  three  feet  above 
the  weir,  the  measurements  of  depth  being  made  from  the  top  of 
this  stake  to  the  surface  of  the  water. 

It  will  be  noted  from  these  conditions  that  the  weir  is  not  a  suit- 
able means  of  measuring  water  under  all  conditions.  In  ditches 
where  the  grade  is  very  slight,  placing  a  bulkhead  across  a  stream 
and  raising  the  level  of  the  water  above  the  weir  often  results  in  a 
break  in  the  ditch  bank.  In  such  cases  it  is  also  difficult  to  keep  the 
weir  from  becoming  submerged. 

In  streams  heavily  laden  with  silt  the  weir  is  not  a  practical 
means  of  measurement.     Reducing  the  velocity  of  the  water  to  the 


Circular  250] 


MEASUREMENT  OF   IRRIGATION  WATER 


point  necessary  for  weir  measurements  soon  precipitates  such  a  quan- 
tity of  solid  matter  above  the  weir  that  suitable  weir  conditions  no 
longer  exist. 

By  itself,  a  weir,  measures  a  rate  of  flow  and  does  not  indicate 
the  total  quantity  delivered.  In  conjunction  with  a  water  register, 
which  keeps  a  graphic  record  of  the  changing  depth  of  water  over 
the  weir,  a  permanent  record  is  obtained  from  which  the  total  quan- 
tity of  water  can  be  easily  computed. 

WEIE   NOTCHES 

There  are  three  types  of  weir  notches  in  common  use,  viz:  rec- 
tangular weirs,  Cipolletti  weirs,  and  triangular  weirs.  Special  tables 
have  been  devised  for  each  of  these.  It  is  of  course  essential  that 
the  proper  table  be  used  for  the  weir  crest  selected.* 


Fig.  2.     Two  foot  rectangular  weir  notch. 


RECTANGULAR  WEIRS 

The  name  is  taken  from  the  shape  of  the  weir  notch,  shown  in 
figure  2.  This  weir  is  also  known  sometimes  as  the  Francis  weir.  It 
is  one  of  the  earliest  forms  of  weirs  used  and  is  the  type  from  which 
all  other  forms  have  been  developed.  Because  of  the  simplicity,  ease 
of  construction,  and  accuracy  with  which  the  crest  and  sides  may  be 
set  with  the  implements  ordinarily  at  hand,  this  type  of  weir  should 
be  used  more  widely  than  it  has  been  in  the  past.  It  is  as  accurate  as 
the  other  types.  The  crest  is  placed  in  a  horizontal  position  and  the 
sides  extend  vertically  above  the  crest.  A  right  angle  is  therefore 
formed,  which  permits  the  weir  to  be  made  and  set  easily  and  accu- 
rately by  means  of  a  carpenter's  square  and  level.  The  sides  must  be 
placed  carefully  to  give  the  desired  length  along  the  crest.  Table  1 
gives  the  discharge  over  rectangular  weirs  from  one  to  four  feet  in 
length,  computed  from  the  corrected  formula: 


*  The  discussion  of  " rectangular  weirs,"  "Cipolletti  weirs''  and  "90-degree 
triangular  notch  weirs,"  together  with  the  discharge  tables  for  these  weir 
notches,  is  copied  largely  from  Farmers'  Bulletin  No.  813,  entitled  "Construc- 
tion and  Use  of  Farm  Weirs, ' '  by  Victor  M.  Cone. 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

TABLE  1 

Discharge  Table  for  Rectangular  Weirs 


Discharge  in 

cubic  feet  per  second 

Discharge  in 

cubic  feet  per  second 

Head 

Head 

for  crests  of  various  lengths 

Head 

Head 

for  crests  of  various  lengths 

in 

in 

in 

in 

feet 

inches 

feet 

inches 

lfoot 

1.5  feet 

2  feet 

3  feet 

4  feet 

lfoot 

1.5  feet 

2  feet 

3  feet 

4  feet 

0.20 

2% 

0.291 

0.439 

0.588 

0.887 

1.19 

.86 

10ft  « 

2.46 

3.72 

5.01 

7.59 

10.19 

.21 

2*4 

.312 

.472 

.632 

.954 

1.28% 

.87 

10ft6 

2.50 

3.79 

5.10 

7.72 

10.36 

.22 

2% 

.335 

.505 

.677 

1.02 

1.37 

.88 

10ft  6 

2.54 

3.85 

5.18 

7.85 

10.54 

.23 

2% 

.358 

.539 

.723 

1.09 

1.46 

.89 

lOlfte 

2.58 

3.92 

5.27 

7.99 

10.71 

.24 

2% 

.380 

.574 

.769 

1.16 

1.55 

.90 

lOHie 

2.62 

3.98 

5.35 

8.12 

10.89 

.25 

3 

.404 

.609 

.817 

1.23 

1.65 

.91 

lOHis 

2.67 

4.05 

5.44 

8.25 

11.07 

.26 

3« 

.428 

.646 

.865 

1.31 

1.75 

.92 

Il*'l6 

2.71 

4.11 

5.53 

8.38 

11.25 

.27 

3% 

.452 

.682 

.914 

1.38 

1.85 

.93 

lifts 

2.75 

4.18 

5.62 

8.52 

11.43 

.28 

3% 

.477 

.720 

.965 

1.46 

1.95 

.94 

11*4 

2.79 

4.24 

5.71 

8.65 

11.61 

.29 

3*4 

.502 

.758 

1.02 

1.53 

2.05 

.95 

11% 

2.84 

4.31 

5.80 

8.79 

11.79 

.30 

3% 

.527 

.796 

1.07 

1.61 

2.16 

.96 

11*4 

2.88 

4.37 

5.89 

8.93 

11.98 

.31 

3% 

.553 

.836 

1.12 

1.69 

2.26 

.97 

11% 

2.93 

4.44 

5.98 

9.06 

12.16 

.32 

3Hi« 

.580 

.876 

1.18 

1.77 

2.37 

.98 

11% 

2.97 

4.51 

6.07 

9.20 

12.34 

.33 

3  Hi  6 

.606 

.916 

1.23 

1.86 

2.48 

.99 

11% 

3.01 

4.57 

6.15 

9.34 

12.53 

.34 

4*i6 

.634 

.957 

1.28 

1.94 

2.60 

1.00 

12 

3.06 

4.64 

6.25 

9.48 

12.72 

.35 

4ft  6 

.661 

.999 

1.34 

2.02 

2.71 

1.01 

12*4 

4.71 

6.34 

9.62 

12.91 

.36 

4%  6 

.688 

1.04 

1.40 

2.11 

2.82 

1.02 

12ft 

4.78 

6.43 

9.76 

13.10 

.37 

4fi  6 

.717 

1.08 

1.45 

2.20 

2.94 

1.03 

12% 

4.85 

6.52 

9.90 

13.28 

.38 

4ft  6 

.745 

1.13 

1.51 

2.28 

3.06 

1.04 

12*4 

4.92 

6.62 

10.04 

13.47 

.39 

4  Hi  6 

.774 

1.17 

1.57 

2.37 

3.18 

1.05 

12% 

4.98 

6.71 

10.18 

13.66 

.40 

4i?i  6 

.804 

1.21 

1.63 

2.46 

3.30 

1.06 

12% 

5.05 

6.80 

10.32 

13.85 

.41 

41%  8 

5*i6 

.833 
.863 

1.26 
1.30 

1.69 
1.75 

2.55 
2.65 

3.42 
3.54 

1.07 
1.08 

12Hie 
12Hi6 

5.12 
5.20 

6.90 
6.99 

10.46 
10.61 

14  04 

.42 

14.24 

.43 

5?i6 

.893 

1.35 

1.81 

2.74 

3.67 

1.09 

13*i6 

5.26 

7.09 

10.75 

14.43 

.44 

5*i 
5% 
5*4 
5% 
5% 
5% 
6 

.924 
.955 
.986 
1.02 
1.05 
1.08 
1.11 

1.40 
1.44 
1.49 
1.54 
1.59 
1.64 
1.68 

1.88 
1.94 
2.00 
2.07 
2.13 
2.20 
2.26 

2.83 
2.93 
3.03 
3.12 
3.22 
3.32 
3.42 

3.80 
3.93 
4.05 
4.18 
4.32 
4.45 
4.58 

1.10 
1.11 
1.12 
1.13 
1.14 
1.15 
1.16 

13ft6 
13ft6 

13ft  6 

13ft6 
13  Hi  e 
13Hie 
13  Hi  e 

5.34 
5.41 
5.48 
5.55 
5.62 
5.69 
5.77 

7.19 
7.28 
7.38 
7.47 
7.57 
7.66 
7.76 

10.90 
11.04 
11.19 
11.34 
11.48 
11.64 
11.79 

14.64 

.45 

14.83 

.46 

15.03 

.47 

15.22 

.48 

15.42 

.49 

15.62 

.50 

15.82 

.51 

6*4 
6*i 
6% 
6*4 

1.15 
1.18 
1.21 
1.25 

1.73 

1.78 
1.84 
1.89 

2.33 
2.40 
2.46 
2.53 

3.52 
3.62 
3.73 
3.83 

4.72 
4.86 
4.99 
5.13 

1.17 
1.18 
1.19 
1.20 

14*i6 
14ft6 
14*i 
14% 

5.84 
5.91 
5.98 
6.06 

7.86 
7.96 
8.06 
8.16 

11.94 
12.09 
12.24 
12.39 

16.02 

.52 

16.23 

.53 

16.43 

.54 

16.63 

.55 

6% 

1.28 

1.94 

2.60 

3.94 

5.27 

1.21 

14*4 

6.13 

8.26 

12.54 

16.83 

.56 

6% 

1.31 

1.99 

2.67 

4.04 

5.42 

1.22 

14% 

6.20 

8.35 

12.69 

17.03 

.57 

6  Hi  6 

1.35 

2.04 

2.74 

4.15 

5.56 

1.23 

14% 

6.28 

8.46 

12.85 

17.25 

.58 

6  Hi  6 

1.38 

2.09 

2.81 

4.26 

5.70 

1.24 

14% 

6.35 

8.56 

12.99 

17.45 

.59 

7*i6 

7ft6 

1.42 
1.45 

2.15 
2.20 

2.88 
2.96 

4.36 
4.47 

5.85 
6.00 

1.25 
1.26 

15 

15*4 

6.43 

8.66 

13.14 
13.30 

17.65 

.60 

17.87 

.61 

7ft  6 

1.49 

2.25 

3.03 

4.59 

6.14 

1.27 

15*4 

13.45 

18.07 

.62 

7ft  6 

1.52 

2.31 

3.10 

4.69 

6.29 

1.28 

15% 

13.61 

18.28 

.63 

7ft  6 

1.56 

2.36 

3.17 

4.81 

6.44 

1.29 

15*4 

13.77 

18.50 

.64 

7  Hi  e 
7  Hi  e 
7  Hi  e 

8ft  6 

8ft  e 

1.60 
1.63 
1.67 
1.71 
1.74 

2.42 
2.47 
2.53 
2.59 
2.64 

3.25 
3.32 
3.40 
3.47 
3.56 

4.92 
5.03 
5.15 
5.26 
5.38 

6.59 
6.75 
6.90 
7.05 
7.21 

1.30 
1.31 
1.32 
1.33 
1.34 

15% 
15% 
15  Hi  e 

15Hie 

161i6 

13.93 
14.09 
14.24 
14.40 
14.56 

18.71 

.65 

18.92 

.66 

19.12 

.67 

19.34 

.68 

19.55 

.69 

8V4 

8% 

1.78 
1.82 

2.70 
2.76 

3.63 
3.71 

5.49 
5.61 

7.36 
7.52 

1.35 
1.36 

16ft  6 
16ft  6 

14.72 
14.88 

19.77 

.70 

19.98 

.71 

8*4 

1.86 

2.81 

3.78 

5.73 

7.68 

1.37 

16ft  6 

15.04 

20.20 

.72 

8% 

1.90 

2.87 

3.86 

5.85 

7.84 

1.38 

16ft6 

15.20 

20.42 

.73 

8% 

1.93 

2.93 

3.94 

5.97 

8.00 

1.39 

16Hi6 

15.36 

20.64 

.74 

8% 
9 

1.97 
2.01 

2.99 
3.05 

4.02 
4.10 

6.09 
6.21 

8.17 
8.33 

1.40 
1.41 

16  Hi  e 
16  Hi  6 

15.53 
15.69 

20.86 

.75 

21.08 

.76 

9*4 

2.05 

3.11 

4.18 

6.33 

8.49 

1.42 

17*i6 

15.85 

21.29 

.77 

9*i 

2.09 

3.17 

4.26 

6.45 

8.66 

1.43 

17ft  6 

16.02 

21.52 

.78 

9% 

2.13 

3.23 

4.34 

6.58 

8.82 

1.44 

17*4 

16.19 

21.74 

79 

9*4 

2  17 

3  29 

4  42 

6  70 

8  99 

1  45 

17% 

16.34 

21.96 

80 

9% 

2  21 

3  35 

4  51 

6  83 

9  16 

1.46 

17*4 

16.51 

22.18 

.81 

9% 

2.25 

3.41 

4.59 

6.95 

9.33 

1.47 

17% 

16.68 

22.41 

.82 

9  HI  e 

2.29 

3.47 

4.67 

7.08 

9.50 

1.48 

17% 

16.85 

22.64 

83 

9  Hi  s 

2  33 

3  54 

4  75 

7  21 

9  67 

1  49 

17% 

17.01 

22.85 

.84 

10*i « 

2.37 

3.60 

4.84 

7.33 

9.84 

1.50 

18 

17.17 

23.08 

.85 

10ft. 

2.41 

3.66 

4.92 

7.46 

10.01 

Circular  250] 


MEASUREMENT  OF  IRRIGATION  WATER 


CIPOLLETTI  WELES 

This  type  of  weir  is  trapezoidal  in  shape,  the  name  "Cipolletti" 
being  that  of  the  Italian  engineer  who  proposed  its  use.  As  shown 
in  figure  3,  the  crest  of  the  weir,  or  bottom  of  the  weir  notch,  must 
be  level,  and  the  sides  placed  on  a  slope  of  one  to  four,  meaning  one 
unit  horizontal  to  four  units  vertical.  The  notch  therefore  is  larger 
than  a  rectangle  with  the  same  crest  length. 

It  is  readily  seen  that  the  Cipolletti  type  of  weir,  or  in  fact  any 
weir  having  sloping  sides,  is  not  so  easy  either  to  construct  or  to 
check  for  accurracy  as  is  the  rectangular  weir.  The  great  popular- 
ity of  the  Cipolletti  weir  is  due  somewhat  to  its  having  been  proposed 


1  ,               ~>r>l/"           ~l 

r% 

T             L 

24*-$$$      J 

^          Yfe^Tf-r .  7T^1         L 

K               J> 

Fig.  3.     Two  foot  Cipolletti  weir  notch. 


at  a  time  when  the  use  of  weirs  for  measuring  irrigation  water  was 
being  considered,  but  principally  because  the  angle  which  the  sides 
make  with  the  crest  was  supposed  to  make  the  flow  over  the  weir 
proportional  to  the  length  of  the  crest.  In  other  words,  the  flow  for 
a  certain  head  on  a  two-foot  weir  was  supposed  to  be  twice  the  flow 
over  a  one-foot  weir  for  the  same  depth  of  water,  which  would  re- 
quire but  a  simple  weir  table  for  field  use.  Recent  experiments, 
however,  prove  that  the  flow  over  Cipolletti  weirs  is  not  proportional 
to  the  length  of  the  crest,  which  apparently  refutes  the  principal 
argument  in  its  favor.  However,  if  the  sides  are  placed  properly 
with  respect  to  the  crest,  and  other  conditions  are  observed  fully, 
the  flow  can  be  measured  as  accurately  over  a  Cipolletti  weir  as  over 
a  rectangular  weir,  by  use  of  the  accompanying  weir  tables,  or  formula. 
It  is  all  right,  therefore,  to  use  a  Cipolletti  weir  if  built  properly,  but 
where  a  weir  is  to  be  constructed,  the  rectangular  should  be  chosen  in 
preference  to  the  Cipolletti  type.  Table  2  gives  the  discharge  over 
Cipolletti  weirs  from  one  to  four  feet  in  length,  computed  from  the 
corrected  formula. 


10 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


TABLE  2 

Discharge  Table  for  Cipolletti  Weirs 


Head 

in 
inches 


Discharge  in  cubic  feet  per  second 
for  crests  of  various  lengths 


2% 
2*4 
2% 
231 
2% 
3 

3% 
3% 
3*4 
3% 
3% 

31?'l6 
315'l6 

4*ie 

43'i6 
49l6 
4?16 

4%e 
4Hie 
4i?i6 

41%6 

5*ie 
59ie 
5% 
5% 
5*4 
5% 
5% 
5% 
6 

6*4 
6% 
614 
6% 
6% 

6^16 

6^16 
71'l6 
7%6 
79'l6 
77/l6 

791e 
7H'i6 
7i?i6 

71%6 
8116 

89ie 

8*4 

8% 

814 

8% 

8% 

8% 

9 

914 

914 

994 

914 

9% 

9% 

9»9'l6 
9^16 

1011s 

109*6 


1  foot  1.5  feet  2  feet 


0.30 

.32 

.35 

.37 

.39 

.42 

.45 

.47 

.50 

.53 

.56 

.59 

.61 

.64 

.67 

.70 

.73 

.77 

.80 

.83 

.87 

.90 

.93 

.97 

1.00 

1.04 

1.07 

1.11 

1.15 

1.18 

1.22 

1.26 

1.30 

1.34 

1.38 

1.42 

1.46 

1.50 

1.54 

1.58 


1 

1 

1 

1 

1 

1 

1.89 

1.93 

1.98 

2.02 

2.07 

2.12 

2.16 

2.21 

2.26 

2.31 

2.36 

2.41 

2.46 

2.51 

2.56 

2.61 

2.66 

2.71 

2.77 

2.82 


0.45 
.48 
.52 
.55 
.59 
.63 
.67 
.70 
..74 
.79 
.83 
.87 
.91 
.95 
1.00 
1.04 
1.09 
1.13 
.1.18 
1.23 
1.28 
1.32 
1.37 
1.42 
1.47 
1.53 
1.58 
1.63 
1.68 
1.74 
1.79 
1.85 
1.90 
1.96 
2.02 
2.07 
2.13 
2.19 
2.25 
2.31 
2.37 
2.43 
2.49 
2.55 
2.62 
2.68 
2.75 
2.81 
2.87 
2.94 
3.01 
3.07 
3.14 
3.21 
3.28 
3.35 
3.42 
3.49 
3.56 
3.63 
3.70 
3.77 
3.84 
3.92 
3.99 
4.07 


0.60 

.64 

.69 

.74 

.79 

.84 

.89 

.94 

.99 

1.04 

1.10 

1.15 

1.21 

1.27 

1.32 

1.38 

1.44 

1.50 

1.57 

1.63 

1.69 

1.76 

1.82 

1.89 

1.95 

2.02 

2.09 

2.16 

2.23 

2.30 

2.37 

2.44 

2.51 

2.59 

2.66 

2.74 

2.81 

2.89 

2.97 

05 


13 

20 

28 

■il 

45 

53 

61 

3.70 

3.79 

3.87 

3.95 

4.04 

4.13 

4.22 

4.31 

4.40 

4.49 

4.58 

4.67 

4.76 

4.85 

4.95 

5.04 

5.14 

5.23 

5.33 


3  feet 


0.90 
.97 
1.04 
1.11 
1.18 
1.25 
1.33 
1.40 
1.48 
1.56 
1.64 
1.73 
1.80 
1.89 
1.98 
2.07 
2.16 
2.25 
2.34 
2.43 
2.53 
2.62 
2.72 
2.81 
2.91 
3.01 
3.11 
3.21 
3.32 
3.42 
3.53 
3.64 
3.74 
3.85 
3.96 
4.07 
4.18 
4.30 
4.41 
4.53 
4.64 
4.76 
4.88 
5.00 
5.12 
5.24 
5.36 
5.48 
5.61 
5.73 
5.86 
5.99 
6.12 
6.24 
6.38 
6.51 
6.64 
6.77 
6.90 
7.04 
7.18 
7.31 
7.45 
7.59 
7.73 
7.87 


4  feet 


1.20 
1.29 
1.38 
1.47 
1.57 
1.67 
1.77 
1.87 
1.97 
2.08 
2.19 
2.30 
2.41 
2.52 
2.64 
2.75 
2.87 
2.99 
3.11 
3.24 
3.36 
3.49 
3.61 


74 
.87 
.01 

14 
.28 
.41 

55 


3. 

3. 
4. 
4. 
4. 
4. 
4. 
4.69 
4.83 
4.97 
5.12 
5.26 
5.41 
5.56 
5.71 
5.86 
6.01 
6.17 
6.32 
6.47 
6.63 
6.79 
6.95 
7.11 
7.28 
7.44 
7.61 
7.77 
7.94 
8.11 
8.28 
8.45 
8.62 
8.80 
8.97 
9.15 
9.33 
9.51 
9.69 
9.87 
10.05 
10.23 
10.42 


Head 
in 

feet 


.86 

.87 

.88 

.89 

.90 

.91 

.92 

.93 

.94 

.95 

.96 

.97 

.98 

.99 

1.00 

1.01 

1.02 

1.03 

1.04 

1.05 

1.06 

1.07 

1.08 

1.09 

1.10 

1.11 

1.12 

1.13 

1.14 

1.15 

1.16 

1.17 

1.18 

1.19 

1.20 

1.21 

1.22 

1.23 

1.24 

1.25 

1.26 

1.27 

1.28 

1.29 

1.30 

1.31 

1.32 

1.33 

1.34 

1.35 

1.36 

1.37 

1.38 

1.39 

1.40 

1.41 

1.42 

1.43 

1.44 

1.45 

1.46 

1.47 

1.48 

1.49 

1.50 


Head 
nches 


lCYie 

10%6 

lOTie 
lOHle 
10'%6 

ioiy16 

lllie 

11316 

1111 

U% 

11*4 

11% 

1194 

11% 

12 

12H 

1214 

1294 

1214 

12% 

1294 

1219!  e 

1219'ie 

1311c 

13916 

13916 

13?16 

139ie 
13H'16 
131916 

13^16 

14*16 

149.6 

1414 

14% 

1414 

14% 

1494 

14% 

15 

1514 

1514 

1594 

1514 

15% 

1594 

151916 

15^16 
16116 

16916 
1691e 
16?i8 
169ie 
16H16 
16*946 

16^16 

17*1 6 

17916 
17*4 
17% 
17*4 
17% 
1794 
17% 
18 


Discharge  in  cubic  feet  per  second 
for  crests  of  various  lengths 


lfoot   1.5  feet  2  feet    3  feet    4  feet 


2.87 
2.93 
2. 98 
3.04 
3.09 
3.15 
3.20 
3.26 
3.32 
3.37 
3.43 
3.49 
3.55 
3.61 
3.67 


4.14 
4.22 
4.29 
4.37 
4.45 
4.53 
4.60 
4.68 
4.76 
4.84 
4.92 
5.00 
5.09 
5.17 
5.25 
5.33 
5.42 
5.50 
5.59 
5.67 
5.76 
5.84 
5.93 
6.02 
6.11 
6.20 
6.29 
6.37 
6.46 
6.56 
6.65 
6.74 
6.83 
6.93 
7.02 
7.11 
7.20 
7.30 
7.40 
7.49 


5.43 
5.52 
5.62 
5.72 
5.82 
5.92 
6.02 
6.13 
6.23 
6.33 
6.44 
6.55 
6.64 
6.75 
6.86 
6.96 
7.07 
7.18 
7.29 
7.40 
7.51 
7.62 
7.73 
7.84 
7.96 
8.07 
8.18 
8.29 
8.41 
8.53 
8.65 
8.76 
8.88 
9.10 
9.12 
9.24 
9.36 
9.48 
9.60 
9.72 


8.01 
8.15 
8.30 
8.44 
8.59 
8.73 
8.88 
9.03 
9.17 
9.32 
9.48 
9.62 
9.78 
9.93 
10.08 
10.24 
10.40 
10.55 
10.71 
10.87 
11.03 
11.18 
11.35 
11.51 
11.68 
11.84 
12.00 
12.16 
12.33 
12.50 
12.67 
12.84 
13.01 
13.18 
13.35 
13.52 
13.69 
13.87 
14.04 
14.21 
14.39 
14.56 
14.74 
14.92 
15.11 
15.29 
15.46 
15.64 
15.82 
16.01 
16.19 
16.37 
16.57 
16.75 
16.94 
17.13 
17.31 
17.51 
17.70 
17.89 
18.08 
18.28 
18.47 
18.66 
18.85 


10.60 
10.79 
10.98 
11.17 
11.36 
11.55 
11.74 
11.94 
12.13 
12.33 
12.53 
12.72 
12.92 
13.12 
13.32 
13.53 
13 .  73 
13.94 
14.15 
14.35 
14.56 
14.76 
14.98 
15.19 
15.41 
15.62 
15.84 
16.04 
16.26 
16.48 
16.70 
16.93 
17.15 
17.37 
17.59 
17.81 
18.03 
18.27 
18.49 
18.71 
18.95 
19.17 
19.41 
19.65 
19.88 
20.12 
20.34 
20.58 
20.82 
21.06 
21.29 
21.53 
21.78 
22.02 
22.27 
22.51 
22.75 
23.01 
23.26 
23.50 
23.75 
24.01 
24.26 
24.50 
24.75 


Circular  250] 


MEASUREMENT  OF  IRRIGATION  WATER 


11 


90-DEGEEE    TEIANGULAE-NOTCH   WEIRS 

This  type  of  weir  (Fig.  4)  deserves  to  be  more  widely  used  than 
at  present  for  the  measurement  of  small  quantities  of  water  to  the 
irrigator.  If  sufficient  fall  is  available  it  may  be  used  for  flows  as 
great  as  fourteen  second-feet,  which  would  be  obtained  with  a  depth 
of  practically  two  feet  of  water  above  the  vertex,  or  lowest  point,  of 
the  angle  formed  by  the  sides.  However,  conditions  usually  are  not 
favorable  for  its  use  for  such  large  heads,  and  table  3  gives  the 
discharge  for  heads  up  to  1.25  feet.  Since  the  sides  meet  at  a  point 
with  no  length  of  crest,  a  small  flow  of  water  that  would  not  pass 
over  one  of  the  other  weirs  without  adhering  to  the  crest  and  therefore 
making  the  measurement  worthless,  will  flow  free  in  the  ninety-degree 


Fig.  4.     90°  weir  notch. 


triangular  notch  and  may  be  measured  accurately.  The  ninety-degree 
triangular  notch  is  especially  applicable  from  small  flows  up  to  two 
or  three  cubic  feet  per  second.  Because  of  the  greater  depth  of  water 
required  for  this  type  of  weir  to  discharge  a  given  quantity  of  water, 
and  the  consequent  greater  loss  of  head,  one  of  the  other  types  of  weirs 
usually  will  be  better  adapted  to  large  quantities  of  water.  Experi- 
ments have  shown  that  the  rectangular  and  Cipolletti  weirs  with  six- 
inch  crest  lengths  do  not  follow  the  same  laws  of  discharge  as  the 
longer  weirs,  and  the  discharge  formulae  given  in  this  circular  for 
these  weirs  do  not  apply  to  weirs  with  a  crest  length  of  six  inches  or 
less.  Therefore,  where  only  a  small  flow  of  water  is  to  be  measured 
the  use  of  the  ninety-degree  triangular  notch  is  especially  recom- 
mended. 

The  sides  of  the  ninety-degree  triangular  notch  may  be  set  read- 
ily by  means  of  a  carpenter's  square  and  level.  The  notch  can  be 
marked  out  properly  by  placing  the  point  of  the  angle  between  the 
arms  of  a  carpenter's  square  at  a  point  which  is  to  be  the  bottom 
of  the  notch  and  adjusting  the  square  so  that  the  same  figures  on 


12 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 


both  arms  of  the  square  are  at  the  edge  of  the  board,  then  if  the 
board  is  set  level  the  notch  will  be  in  the  proper  position.  The  sides, 
therefore,  have  the  same  slope. 

Table  3   gives  the  discharge   over  the   ninety-degree   triangular 
notch,  computed  from  the  corrected  formula: 

TABLE  3 

Discharge  Table  for  90°  Triangular  Notch 


Discharge 

Discharge 

Discharge 

Head  in 

Head  in 

in  second- 

Head  in 

Head  in 

in  second- 

Head  in 

Head  in 

in  second- 

feet 

inches 

feet  (Q) 

feet 

inches 

feet  (Q) 

feet 

inches 

feet  (Q) 

0.20 

2% 

0.046 

0.55 

6% 

0.564 

0.90 

101?'l6 

1.92 

.21 

2*4 

.052 

.56 

6% 

.590 

.91 

ioiy,6 

1.97 

.22 

2% 

.058 

.57 

6^8 

.617 

.92 

lUie 

2.02 

.23 

2% 

.065 

.58 

m* 

.644 

.93 

11%6 

2.08 

.24 

2% 

.072 

.59     . 

7Via 

.672 

.94 

11% 

2.13 

.25 

3 

.080 

.60 

7%6 

.700 

.95 

11% 

2.19 

.26 

3% 

.088 

.61 

7%a 

.730 

.96 

n% 

2.25 

.27 

3% 

.096 

.62 

7yi6 

.760 

.97 

n% 

2.31 

.28 

3% 

.106 

.63 

7%6 

.790 

.98 

n% 

2.37 

.29 

3*4 

.115 

.64 

7Hi6 

.822 

.99 

n% 

2.43 

.30 

3% 

.125 

.65 

7Mia 

.854 

1.00 

12 

2.49 

.31 

3% 

.136 

.66 

7Hia 

.887 

1.01 

12% 

2.55 

.32 

3i?ic 

.147 

.67 

8Vi6 

.921 

1.02 

12% 

2.61 

.33 

3^16 

.159 

.68 

8%8 

.955 

1.03 

12% 

2.68 

.34 

4H« 

.171 

.69 

8*4 

.991 

1.04 

12% 

2.74 

.35 

4%6 

.184 

.70 

8% 

1.03 

1.05 

12% 

2.81 

.36 

4<j'l6 

.197 

.71 

8tf 

1.06 

1.06 

12% 

2.87 

.37 

4%a 

.211 

.72 

8% 

1.10 

1.07 

12i%6 

2.94 

.38 

4?i6 

.226 

.73 

8% 

1.14 

1.08 

12i%6 

3.01 

.39 

4Hie 

.240 

.74 

8% 

1.18 

1.09 

13%6 

3.08 

.40 

4% 

.256 

.75 

9 

1.22 

1.10 

13%6 

3.15 

.41 

4% 

.272 

.76 

9tf 

1.26 

1.11 

13%6 

3.22 

.42 

5Vie 

.289 

.77 

9% 

1.30 

1.12 

13%6 

3.30 

.43 

5«a 

.306 

.78 

9% 

1.34 

1.13 

13%6 

3.37 

.44 

5% 

.324 

.79 

9*4 

1.39 

1.14 

131%6 

3.44 

.45 

5% 

.343 

.80 

9% 

1.43 

1.15 

13Mi6 

3.52 

.46 

5% 

.362 

.81 

9% 

1.48 

1.16 

13i%6 

3.59 

.47 

5% 

.382 

.82 

99ia 

1.52 

1.17 

14Ko 

3.67 

.48 

5% 

.403 

.83 

9*%6 

1.57 

1.18 

14%6 

3.75 

.49 

5% 

.424 

.84 

10*ia 

1.61 

1.19 

14% 

3.83 

.50 

6 

.445 

.85 

10?ia 

1.66 

1.20 

14% 

3.91 

.51 

6% 

.468 

.86 

10%a 

1.71 

1.21 

14% 

3.99 

.52 

6*4 

.491 

.87 

10'/l6 

1.76 

1.22 

14% 

4.07 

.53 

6% 

.515 

.88 

1015a 

1.81 

1.23 

14% 

4.16 

.54 

6% 

.539 

.89 

lOHis 

1.86 

1.24 
1.25 

14% 
15 

4.24 
4.33 

WEIR  CONSTRUCTION 

The  type  of  the  soil  in  which  a  weir  is  to  be  placed  is  important 
in  determining  whether  a  simple  weir  board  or  a  more  elaborate 
weir  box  should  be  used.  In  heavy  clay  soils  where  excessive  wash- 
ing of  the  soil  does  not  occur,  a  simple  bulkhead  placed  across  the 
stream  can  be  used.  In  lighter  soils  where  the  washing  out  of  ditch 
structures  is  liable  to  occur,  a  weir  box  is  necessary. 

Figure  5  is  an  isometric  drawing  of  a  simple  weir  bulkhead  which 
can  be  easily  constructed  on  the  farm.     Table  4  gives  the  sizes  of 


Circular  250] 


MEASUREMENT  OF  IRRIGATION  WATER 


13 


weirs  and  weir  bulkheads  best  adapted  for  the  measuring  of  heads 
of  water  from  one-half  cubic  foot  per  second  to  thirteen  cubic  feet 
per  second.  The  letters  at  the  heads  of  the  columns  refer  to  the 
dimensions  as  shown  in  figure  5 : 


"*^^ 

'    r-%       "\s4M& 

J\ 

f 

^T^***^'-              r-a  . 

ior/tJ'i^' 

■%  / 

si            » 

"*                  H                   *" 

C 

1 

_  _G 

"1 

/ 

/ 

< 

D 

K 

U 

Fig.  5.     Isometric  drawing  of  weir  bulkhead.     Suitable  only  for  rather  heavy  soil. 


TABLE  4 
Weir  Board  Dimensions  tor  Rectangular  and  Cipolletti  Weirs 
Letters  at  head  of  columns  refer  to  figure  5. 


Total 

Distance 

Distance  of 

Capacity 

Maximum 

Total 

length  of 

of  crest, 

edge  of 

of  weir, 

Length 

head  over 

Depth 

depth  of 

bulk- 

G, above 

Length 

notch,  F, 

cubic  feet 

of  crest, 

weir  crest, 

of  notch, 

bulkhead 

head, 

ditch 

of  wing, 

from  ditch 

per  second 

A,  feet 

B,  feet 

H,  feet 

C,  feet 

D,  feet 

bottom,  ft. 

E,  feet 

bank,  feet 

Hto2 

1.5 

.56 

1.0 

3.0 

10.0 

0.3 

4.25 

1.5 

1      to  7V2 

3.0 

.86 

1.0 

4.0 

12.0 

0.5 

4.50 

2.0 

\Yt  to  13 

4.0 

1.00 

1.5 

5.0 

16.0 

0.7 

6.00 

2.5 

With  rectangular  or  Cipolletti  weirs,  as  previously  stated,  the 
head  of  water  can  best  be  measured  from  a  stake  driven  in  the  ditch 
bank  or  bottom  to  the  elevation  of  the  weir  crest  and  about  three 
feet  upstream  from  the  crest.  The  stake  can  be  easily  set  with  an 
accurate  carpenter's  level.  The  depth  of  water  over  this  stake,  as 
shown  by  a  carpenter's  rule,  will  then  measure  the  depth  of  water 
passing  over  the  weir. 

Figure  6  shows  the  construction  of  a  complete  weir  box.  The 
letters  refer  to  table  5,  which  shows  the  dimensions  of  these  boxes  as 
built  for  measuring  heads  of  water  from  one-half  cubic  foot  per 
second  to  seventeen  cubic  feet  per  second: 


14 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


TABLE  5 

Dimensions  for  Weir  Boxes  as  Shown  in  Figure  6 
Letters  at  head  of  columns  refer  to  figure  6. 


Distance 

of  crest 

Maxi- 

Total 

Total 

Total 

Distance 

Edge  of 

above 

Capacity 

mum 

depth 

depth 

length 

of  crest 

notch, 

Distance 

overflow 

of  weir, 

Length 

head 

of 

of 

of 

above 

Length 

F,  from 

between 

of 

cubic 

of 

over 

notch, 

bulk- 

bulk- 

ditch 

of 

ditch 

bulk- 

water 

feet  per 

crest, 

weir, 

H, 

head, 

head, 

bottom, 

wing, 

bank, 

heads, 

cushion, 

second 

A,  feet 

B,  feet 

feet 

C,  feet 

D,  feet 

G,  feet 

E,  feet 

feet 

I,  feet 

M,  feet 

Hto2H 

1.5 

.67 

1.0 

3.0 

10.0 

0.3 

4.25 

1.5 

3.0 

1.0 

2  to  7V2 

3.0 

.86 

1.0 

4.0 

12.0 

0.5 

4.50 

2.0 

3.0 

1.2 

6  to  17 

4.0 

1.20 

1.5 

5.0 

16.0 

0.7 

6.00 

2.5 

3.5 

1.4 

Note. — In  all  cases  assumed  in  figure  6  the  water  cushion  below  the  weir  crest  is  6  inches  deep, 
although  any  depth  that  will  give  sufficient  pool  to  break  the  fall  of  the  water,  in  order  to  prevent 
ditch  erosion  below,  is  satisfactory.  The  overflow  from  this  cushion  should  be  on  the  grade  of  the 
ditch  bottom  as  it  leaves  the  structure.  In  the  last  column  of  the  table,  definite  distances  of  crest, 
M,  above  the  overflow  of  the  water  cushion  are  assumed,  because  these  distances  are  ample.  Any 
drop,  however,  that  permits  a  free  fall  of  the  water  over  the  weir  crest  meets  the  conditions  required 
by  the  weir  formula. 

SUBMERGED  ORIFICES 

In  cases  where  the  grade  of  ditch  is  so  flat  that  the  required  free 
fall  over  a  weir  can  not  be  easily  obtained,  and  in  cases  where  the 
waters  are  so  heavily  charged  with  silt  that  there  is  danger  of  a 
weir  pond  silting  up,  some  type  of  submerged  orifice  is  commonly 
used. 

The  measurement  of  water  through  orifices  has  long  been  com- 
mon in  irrigation  practice  and  various  forms  of  orifices  have  been 


Fig.  6.     Isometric  drawing  of  weir  bulkhead.     Designed  for  light  soils. 


Circular  250] 


MEASUREMENT  OF  IRRIGATION  WATER 


15 


developed.  The  essential  condition  in  the  use  of  an  orifice,  eliminat- 
ing the  question  of  form,  is  that  the  water  on  the  up-stream  side  of 
the  orifice  shall  completely  submerge  it.  If,  when  in  use,  the  surface 
of  the  water  on  the  lower  side  of  the  orifice  is  below  the  bottom 
thereof,  the  orifice  is  said  to  have  a  free  discharge.  If  the  surface 
of  the  water  on  the  lower  side  of  the  orifice  is  above  the  top  of  the 


rCaRPENTdR's  RULE                                                                                                   Caf?PENT£R'S^R(JLEp 

^x 

1 

_1_ 

"h" 

: 

^d 

\ 

- 

^~ 

. ^- 

Y        ?'        I 

. 

.— , 

r           J            1 

*                  3              ■     H 

t   1 

4 

i                                               '  ' 
Sr/7/f/r -^J,   \ 

ij 

Fig.  7.     Diagrammatic  sketch  showing  orifice  of  fixed  dimensions  in  use. 


Tig.  8.    Isometric  drawing  of  U.S.R.S.  submerged  orifice. 


16  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

orifice,  completely  submerging  it,  it  is  classed  as  a  submerged  ori- 
fice. Except  in  the  case  of  the  miner's  inch  box,  which  is  really 
but  a  form  of  orifice  with  free  discharge,  use  of  the  orifice  in  irri- 
gation practice  is  mainly  confined  in  California  to  the  submerged 
form. 

Submerged  orifices  as  used  can  be  divided  into  two  general  types, 
viz:  those  with  orifices  of  fixed  dimensions  (Fig.  8)  and  those  built 
so  that  the  height  of  the  opening  may  be  varied   (Figs.  9  and  10). 


Fig.  9.     Photograph  of  adjustable  submerged  orifice  in  use. 

Orifices  of  fixed  dimensions  are  usually  made  with  sharp  edges  simi- 
lar to  the  crest  of  a  weir.  The  most  usual  type  of  adjustable  ori- 
fice is  the  simple  head  gate,  the  height  of  opening  and  loss  of  head 
being  adjusted  to  the  amount  which  it  is  desired  to  turn  out  and 
to  the  loss  of  head  available.  Of  these  two  types,  the  sharp-edged 
orifice  of  fixed  dimensions  is  much  the  more  accurate  in  practice. 

With  either  of  these  types  of  submerged  orifice,  the  quantity  of 
water  passing  through  the  orifice  is  measured  by  the  difference  in 
water  level  above  and  below  the  orifice.  Such  a  difference  in  water 
level  always  exists  in  devices  of  this  sort.  This  difference  in  water 
level  is  commonly  called  the  "difference  in  head"  or  "loss  of  head." 
A  small  "la"  is  usually  used  to  represent  this  difference. 

Figure  7  is  a  diagramatic  sketch  of  a  submerged  orifice  in  use. 

The  amount  of  water  which  passes  through  a  submerged  orifice 
of  fixed  dimensions  increases  as  "h"   increases.     Theoretically,  if 


Circular  250] 


MEASUREMENT  OF  IRRIGATION  WATER 


17 


"h"  could  be  indefinitely  increased,  any  quantity  of  water  could  be 
passed  through  an  orifice  with  an  area  of  one  square  foot.  Practical 
difficulties  make  it  impossible  for  this  difference  in  head  in  small 
ditches  ever  to  become  larger  than  about  eighteen  inches.  In  ditches 
on  very  flat  grades  this  difference  in  head  can  not  become  more  than 
four  or  five  inches  without  endangering  the  ditch  bank  above  the 
orifice. 


Fig.  10.     Isometric  drawing  of  adjustable  submerged  orifice. 


In  cases  where  sufficient  discharge  can  not  be  obtained  through 
the  orifice  with  the  loss  in  head  that  is  permissible,  a  larger  orifice 
may  be  used.     With  a  given   difference  in  head,   the  discharge  is 
directly  proportional  to  the  area  of  the  orifice  and  unreasonable  dif-  / 
ference  in  head  can  be  reduced  by  increasing  this  area.* 


*  With  crude  adjustable  submerged  orifices,  the  statement  that  the  discharge 
for  a  given  loss  of  head  is  directly  proportional  to  the  area  of  the  orifice  is  not 
strictly  true.  Work  done  by  the  Kern  County  Land  Company  shows  that  the 
value  of  "C"  in  the  formula  v=C  \/2g~h  varies  with  changes  in  the  area  of 
the  opening.     The  exact  proportion  is  consequently  destroyed. 


18  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


SUBMEEGED  OKIFICE  WITH  FIXED  DIMENSIONS 

This  type  of  submerged  orifice  is  used  for  measurements  only, 
the  fixing  of  the  size  of  the  opening  preventing  its  use  as  a  headgate. 

In  order  that  the  known  formulae  for  the  discharge  through  such 
orifices  shall  apply,  certain  standard  conditions  must  be  observed  in 
their  construction  and  use.  The  edges  of  the  orifice  must  be  sharp 
and  definite  in  shape.  It  is  preferable  to  use  a  thin  metal  plate  as 
this  is  not  subject  to  wear  and  change.  The  edges  of  the  orifice 
should  not  be  too  near  to  the  sides  of  the  box  on  either  the  upper  or 
lower  sides;  a  distance  equal  to  twice  the  least  dimension  of  the  ori- 
fice is  sufficient.  The  sides  of  the  orifice  should  be  vertical  and  the 
bottom  edge  level.  The  ditch  above  the  orifice  should  be  sufficiently 
large  so  that  the  velocity  of  approach  will  be  small,  as  is  necessary 
in  the  case  of  a  weir.  Corrections  can  be  made  in  the  computations 
for  any  velocity  of  approach  but  such  corrections  are  more  or  less 
uncertain. 

The  principal  sources  of  error  in  measurements  with  this  type 
of  orifice  are  due  to  errors  in  the  gauge  readings  to  determine  the 
difference  in  the  elevation  of  the  water  on  the  two  sides,  this  being 
the  head  or  pressure  that  forces  the  water  through  the  orifice.  As 
these  orifices  are  generally  used  where  there  is  but  little  loss  of  head 
available,  the  opening  is  usually  made  sufficiently  large  to  require 
as  little  loss  of  head  as  is  practicable.  Any  error  in  reading  this 
small  loss  of  head  is  thus  a  larger  percentage  of  the  whole  than  it 
would  be  for  greater  total  differences. 

In  the  use  of  the  submerged  orifice  two  gauge  readings  are  re- 
quired, one  above  and  one  below  the  orifice.  The  reading  above  the 
orifice  should  be  taken  back  from  the  edge  of  the  orifice.  In  the  type 
of  structure  shown  in  figures  8  and  10  this  can  be  taken  on  the  side 
wing  wall.  Perhaps  a  still  better  way  is  to  drive  two  stakes  in  the 
bottom  of  the  ditch,  one  of  which  should  be  about  three  feet  above 
the  orifice  and  the  other  three  feet  below.  By  driving  these  stakes 
to  the  same  elevation  and  measuring  the  depth  of  water  over  each 
of  them,  the  difference  in  head  or  "h"  can  be  easily  determined. 
This  quantity  is,  of  course,  the  difference  between  these  two  depths. 

The  type  of  orifice  described  above  and  illustrated  in  figure  8 
has  been  adopted  by  the  United  States  Reclamation  Service  for  use 
where  sufficient  loss  of  head  is  not  available  for  weirs.  The  data 
given  below  regarding  the  sizes  of  the  structures,  and  the  table  of 
discharges  (table  6)  are  taken  from  the  publication  of  the  Reclama- 
tion Service  on  the  measurement  of  irrigation  water  and  from  their 


Circular  250] 


MEASUREMENT  OF  IRRIGATION  WATER 


19 


standard  plans  for  submerged  orifices.     The  cost  of  one  of  these  de- 
vices installed  will  vary  from  about  $10  to  $30. 


TABLE  6 

Discharge  of  Submerged  Eectangular  Orifices  in  Cubic  Feet  per  Second 

Taken  from  il Hydraulic  and  Excavation  Tables' '  published  by  the 

U.  S.  Eeclamation  Service 


Head  h, 

Head  h, 
feet 

Cross-sectional  area  A  of  orifice 

,  square  feet 

inches 

0.25 

0.5 

0.75 

1.0 

1.25 

1.5 

1.75 

2.0 

ft 

0.01 

0.122 

0.245 

0.367 

0.489 

0.611 

0.734 

0.856 

0.978 

ft 

.02 

0.173 

0.346 

0.518 

0.691 

0.864 

1.037 

1.210 

1.382 

ft 

.03 

0.212 

0.424 

0.635 

0.847 

1.059 

1.271 

1.483 

1.694 

ft 

.04 

0.245 

0.489 

0.734 

0.978 

1.223 

1.468 

1.712 

1.957 

ft 

.05 

0.273 

0.547 

0.820 

1.093 

1.367 

1.640 

1.913 

2.186 

ft 

.06 

0.300 

0.599 

0.899 

1.198 

1.497 

1.797 

2.097 

2.396 

»ft« 

.07 

0.324 

0.647 

0.971 

1.294 

1.617 

1.941 

2 .  265 

2.588 

«Ka 

.08 

0.346 

0.691 

1.037 

1.383 

1.729 

2.074 

2.420 

2.766 

1«6 

.09 

0.367 

0.734 

1.101 

1.468 

1.835 

2.201 

2  638 

2.935 

lft« 

.10 

0.387 

0.773 

1.160 

1.557 

1.933 

2.320 

2.707 

3.094 

lfts 

.11 

0.406 

0.811 

1.217 

1.622 

2.027 

2.433 

2.839 

3.244 

lgi 

.12 

0.424 

0.847 

1.271 

1.694 

2.118 

2.542 

2.965 

3.389 

1«16 

.13 

0.441 

0.882 

1.323 

1.764 

2.205 

2.645 

3.086 

3.527 

1% 

.14 

0.458 

0.915 

1.373 

1.830 

2.287 

2.745 

3.203 

3.660 

1^6 

.15 

0.474 

0.947 

1.421 

1.895 

2.369 

2.842 

3.316 

3.790 

l*Si« 

.16 

0.489 

0.978 

1.467 

1.956 

2.445 

2.934 

3.423 

3.912 

2fte 

.17 

0 .  504 

1.008 

1.512 

2.016 

2.520 

3.024 

3.528 

4.032 

2ft« 

.18 

0.519 

1.037 

1.556 

2.075 

2.593 

3.112 

3.631 

4.150 

2% 

.19 

0.533 

1.066 

1.599 

2.132 

2.665 

3.198 

3.731 

4.264 

2% 

.20 

0.547 

1.094 

1.641 

2.188 

2.735 

3.282 

3.829 

4.376 

2ft 

.21 

0.561 

1.120 

1.681 

2.241 

2.801 

3.361 

3.921 

4.482 

2% 

.22 

0.574 

1.148 

1.722 

2.926 

2.870 

3.464 

4.018 

4.592 

2% 

.23 

0.587 

1.172 

1.759 

2.345 

2.931 

3.517 

4.103 

4.690 

2% 

.24 

0.600 

1.198 

1.797 

2.396 

2.995 

3.599 

4.193 

4.792 

3 

.25 

0.612 

1.223 

1.834 

2.446 

3.057 

3.668 

4.280 

4.891 

3ft 

.26 

0.624 

1.247 

1.871 

2.494 

3.117 

3.741 

4.365 

4.988 

3ft 

.27 

0.636 

1.270 

1.906 

2.541 

3.176 

3.811 

4.446 

5.082 

3% 

.28 

0.646 

1.294 

1.942 

2.589 

3.236 

3.883 

4.530 

5.178 

3ft 

.29 

0.659 

1.319 

1.978 

2.638 

3.297 

3.956 

4.616 

5.276 

3% 

.30 

0.670 

1.339 

2.009 

2.678 

3.347 

4.017 

4.687 

5.356 

3% 

.31 

0.681 

1.363 

2.045 

2.726 

3.407 

4.089 

4.771 

5.452 

3i?i6 

.32 

0.692 

1.382 

2.073 

2.764 

3.455 

4.146 

4.837 

5.528 

3%i 

.33 

0.703 

1.405 

2.107 

2.810 

3.513 

4.215 

4.917 

5.620 

4fte 

.34 

0.713 

1.426 

2.139 

2.852 

3.565 

4.278 

4.991 

5.704 

4%e 

.35 

0.724 

1.446 

2.169 

2.892 

3.615 

4.338 

5.061 

5.784 

4yl6 

.36 

0.734 

1.467 

2.201 

2.934 

3.667 

4.401 

5.135 

5.868 

4%a 

.37 

0.745 

1.488 

2.232 

2.976 

3.720 

4.464 

5.208 

5.952 

4?'l6 

.38 

0.754 

1.508 

2.262 

3.016 

3.770 

4.524 

5.278 

6.032 

4Hi6 

.39 

0.764 

1.527 

2.291 

3.054 

3.818 

4.582 

5.345 

6.109 

4»«6 

.40 

0.774 

1.547 

2.321 

3.094 

3.867 

4.641 

5.415 

6.188 

4^16 

.41 

0.783 

1.567 

2.350 

3.133 

3.917 

4.700 

5.483 

6.266 

5fta 

.42 

0.792 

1.585 

2.377 

3.170 

3.962 

4.754 

5.547 

6.339 

5ft« 

.43 

0.802 

1.604 

2.406 

3.208 

4.010 

4.812 

5.614 

6.416 

5ft 

.44 

0.811 

1.622 

2.433 

3.244 

4.055 

4.866 

5.677 

'  6.488 

5% 

.45 

0.820 

1.640 

2.461 

3.281 

4.101 

4.921 

5.741 

6.562 

5ft 

.46 

0.829 

1.659 

2.489 

3.318 

4.147 

4.977 

5.807 

6.636 

5% 

.47 

0.839 

1.678 

2.517 

3.356 

4.195 

5.035 

5.874 

6.713 

5% 

.48 

0.847 

1.695 

2.542 

3.389 

4.237 

5.084 

5.931 

6.778 

5% 

.49 

0.856 

1.712 

2.568 

3.424 

4.280 

5.136 

5.992 

6.848 

6 

.50 

0.865 

1.729 

2.594 

3.458 

4.323 

5.188 

6.052 

6.917 

6ft 

.51 

0.873 

1.746 

2.620 

3.493 

4.366 

5.239 

6.112 

6.986 

6ft 

.52 

0.882 

1.763 

2.645 

3.527 

4.409 

5.290 

6.172 

7.054 

6% 

.53 

0.890 

1.780 

2.670 

3.560 

4.451 

5.341 

6.231 

7.121 

6ft 

.54 

0.898 

1.797 

2.695 

3.593 

4.491 

5.390 

6.288 

7.186 

6ft 

.55 

0.907 

1.813 

2.719 

3.626 

4.533 

5.439 

6.345 

7.252 

6% 

.56 

0.915 

1.830 

2.745 

3.660 

4.575 

5.490 

6.405 

7.320 

6% 

.57 

0.923 

1.846 

2.769 

3.692 

4.615 

5 .  538 

6.461 

7.384 

6«i6 

.58 

0.931 

1.862 

2.794 

3.725 

4.656 

5.587 

6.518 

7.450 

7ft8 

.59 

0.939 

1.879 

2.818 

3.757 

4.697 

5.636 

6.575 

7.514 

7%« 

.60 

0.947 

1.895 

2.842 

3.790 

4.737 

5.684 

6.632 

7.579 

7*a 

.61 

0.955 

1.910 

2.865 

3.820 

4.775 

5.730 

6.685 

7.640 

7ft« 

.62 

0.963 

1.925 

2.887 

3.850 

4.812 

5.775 

6.737 

7.700 

79is 

.63 

0.971 

1.941 

2.911 

3.882 

4.853 

5.823 

6.793 

7.764 

7Hi« 

.64 

0.978 

1.956 

2.934 

3.912 

4.890 

5.868 

6.846 

7.824 

7% 

.65 

0.986 

1.972 

2.958 

3.944 

4.930 

5.916 

6.902 

7.888 

20 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 


CONSTBUCTION    OF   SUBMEKGED    OEIFICES    OF    FIXED   DIMENSIONS 

Figure  8  is  an  isometric  drawing  of  the  type  of  submerged  orifice 
in  use  on  many  of  the  United  States  Reclamation  Service  projects. 
Particular  attention  is  called  to  the  box  below  the  orifice  into  which 
the  water  flows  as  it  passes  through  the  opening.  Such  construction 
adds  strength  to  the  structure,  minimizes  the  danger  of  its  washing 
out  and  lessens  erosion  below  it. 

Since  structures  of  this  sort  must  be  built  in  various  sizes  to 
correspond  to  local  conditions,  the  dimensions  on  the  drawing  (Fig. 
8)  are  indicated  by  letters.  The  letters  refer  to  table  7,  which  gives 
these  dimensions  in  feet  for  boxes  with  various  sizes  of  opening.  In 
all  cases,  the  width  of  the  head  wall  must  be  great  enough  to  extend 
across  the  ditch  from  the  center  line  of  the  ditch  bank  on  one  side 
to  the  center  line  of  the  ditch  bank  on  the  other  side. 

TABLE  7 

Dimensions  for  Standard  Sizes  of  Submerged  Eectangular  Orifices 

Letters  showing  dimensions  refer  to  figure  8. 


Size  of  Orifice 

Head- 

Total 

Bottom 
of  orifice 

wall 
height, 

Box 

height, 

Structure 
length, 

Floor 
width, 

width 
of 

Length 
of  wing, 

above 

ditch 

Height 

Length 

Area, 

B,  feet 

J,  feet 

G,  feet 

D,  feet 

structure 

C,  feet 

bottom, 

F,  feet 

E,  feet 

sq.  feet 

A,  feet 

H,  feet 

.25 

1.0 

.25 

4.5 

2.5 

3.5 

2.0 

8.0 

3.0 

.25 

.25 

2.0 

.50 

4.5 

2.5 

3.5 

3.0 

10.0 

3.5 

.25 

.25 

3.0 

.75 

4.5 

2.5 

3.5 

4.0 

12.0 

4.0 

.25 

.50 

1.0 

.50 

4.5 

2.5 

3.5 

2.0 

8.0 

3.0 

.50 

.50 

1.50 

.75 

4.5 

2.5 

3.5 

2.5 

10.0 

3.75 

.50 

.50 

2.0 

1.00 

4.5 

2.5 

3.5 

3.0 

10.0 

3.5 

.50 

.50 

2.5 

1.25 

4.5 

2.5 

3.5 

3.5 

12.0 

4.25 

.50 

.50 

3.0 

1.50 

5.0 

2.5 

3.5 

4.0 

12.0 

4.0 

.50 

.75 

1.33 

1.00 

4.5 

2.5 

4.0 

2.5 

10.0 

3.75 

.70 

.75 

1.67 

1.25 

4.5 

2.5 

4.0 

3.0 

12.0 

4.5 

.70 

.75 

2.00 

1.50 

4.5 

2.5 

4.0 

3.5 

14.0 

5.25 

.70 

.75 

2.33 

1.75 

5.0 

3.0 

4.0 

3.5 

14.0 

5.25 

.70 

.75 

2.67 

2.00 

5.0 

3.0 

4.0 

4.0 

14.0 

5.0 

.70 

COMPUTATIONS   IF  TABLES  AEE  NOT  AVAILABLE 

One  of  the  advantages  of  the  submerged  orifice  as  a  measuring  de- 
vice lies  in  the  fact  that  tables  are  not  absolutely  necessary  for  a 
ready  determination  of  the  discharge.     The  two  basic  formulae  are: 

Q  =  AV_ 
Vr=CV2gh 
Where      Q  =  discharge  in  cubic  feet  per  second 
A  =  area  of  orifice  in  square  feet 

V  =  velocity  of  water  through  opening  in  feet  per  second 
C  =  a  coefficient  which  is  0.61  for  a  sharp-edged  fixed  opening 
g  =  acceleration  of  gravity  or  32.16  feet  per  second 
h  =  difference  in  head  in  feet 


Circular  250]  MEASUREMENT  OF  IRRIGATION  WATER  21 

These  two  formulae  can  be  combined  into  a  single   expression 

Q  =  AX  4.89  X  Vh 

With  any  sharp-edged  fixed  orifice,  the  square  root  of  the  dif- 
ference in  head,  in  feet  or  fractions  of  feet,  above  and  below  the 
orifice,  multiplied  by  4.89,  multiplied  by  the  area  of  the  opening  in 
square  feet,  will  give  the  discharge  through  the  opening  in  cubic 
feet  per  second. 

Example : 

Area  of  opening  =  2  square   feet 

Measured  difference  in  head  =  0.35  feet 

Discharge  =  2  X  4.89  X  a/0.35  =  5.78   cubic   feet   per   second. 

ADJUSTABLE  SUBMERGED  OEIFICE 

A  submerged  orifice  with  a  fixed  opening  is  evidently  unsuited 
to  streams  which  are  subject  to  wide  fluctuations  in  discharge.  For 
such  conditions,  a  submerged  orifice  with  an  adjustable  opening  has 
been  designed  so  that  varying  heads  may  be  accommodated  without 
endangering  the  banks  of  the  canal.  Such  devices  are  in  common 
use  on  many  irrigation  ditches. 

The  method  of  measurement  for  the  determination  of  the  differ- 
ence in  head  is  similar  to  that  for  the  fixed  orifice.  In  most  cases 
the  size  of  the  opening  can  be  adjusted  by  raising  a  gate  which  slides 
between  guides  nailed  to  the  sides  of  the  box.  In  such  gates  as  this 
the  size  of  the  opening  can  easily  be  determined  by  calibrating  the 
staff  which  raises  the  gate.  A  few  measurements  will  determine  how 
many  square  inches  are  added  to  the  opening  for  each  inch  that  the 
staff  on  the  gate  is  raised.  In  many  cases  the  adjustable  gate  is  held 
in  place  by  a  bolt  which  slips  through  one  of  the  holes  on  the  staff 
of  the  gate  and  through  the  cross  beam  on  the  box.  Since  these  holes 
are  fixed,  the  hole  through  which  the  bolt  passes  is  at  once  evidence 
as  to  the  number  of  square  inches  in  the  opening.  Labeling  these 
holes  with  their  respective  openings  does  away  with  the  necessity  of 
repeated  measurement.  Figure  10  shows  a  gate  arranged  for  this 
means  of  determining  the  size  of  the  opening. 

The  additional  strength  necessary  for  this  adjustable  gate  makes  it 
necessary  that  an  adjustable  submerged  orifice  be  built  in  a  section  of 
flume  or  a  box  in  place  of  a  single  wall  placed  across  the  stream. 
Figure  10  is  an  isometric  drawing  of  a  submerged  orifice  placed  in  a 
flume  and  of  a  size  sufficient  for  discharges  varying  from  one  half 
cubic  foot  per  second  to  twenty  cubic  feet  per  second. 


22  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

The  accurate  measurement  of  water  through  an  adjustable  sub- 
merged orifice  can  not  be  expected  unless  the  individual  structure  has 
been  rated  in  place.  Conditions  do  not  often  permit  the  rating  of 
orifices  in  the  field.  It  has  been  found  that  variations  in  the  structures, 
especially  if  built  by  carpenters  with  different  degrees  of  skill,  the 
cross  section  of  the  canal  immediately  above  the  structure,  the  velocity 
of  the  water  as  it  approaches  the  structure,  and  the  degree  of  sub- 
mergence of  the  orifice  itself  may  all  affect  the  discharge  through  the 
orifice  even  if  the  area  of  the  opening  and  the  difference  in  head  may 
be  constant. 

For  these  reasons  a  table  of  discharge  for  adjustable  submerged 
orifices  would  have  but  little  value  because  of  the,  at  present,  unavoid- 
able error  which  would  be  introduced.  The  discharge  can,  however, 
be  quite  easily  computed.  Such  computations  are  sufficiently  accurate 
for  most  purposes. 

Computation  of  discharge  through  adjustable  submerged  orifices. — 
The  theory  underlying  the  flow  of  water  through  adjustable  orifices 
is  the  same  as  for  fixed  orifices.    The  same  formulae  apply : 

v  =  cvlTgh 

Or 


Q  =  ACX  V2gh 
Or 

Q-AC  8.02  V  h 
Where 

Q  =  discharge  in  cubic  feet  per  second 

A  =  area  of  the  orifice  in  square  feet 

V  =  velocity  of  the  stream  flowing  through  the  orifice,  in  feet  per 
second 

C  =  a  variable  coefficient. 

g  =z  acceleration  of  gravity,  32.16  feet  per  second 

h  =  difference  in  head  in  feet. 

If  the  measurements  of  the  area  of  the  opening  and  the  resulting 
difference  in  head  are  correctly  made,  the  accuracy  of  the  device 
depends  upon  selecting  the  proper  value  for  the  coefficient  C  for  the 
existing  conditions.  Experiments  conducted  in  the  field  laboratory  at 
Davis,  California,  and  in  the  hydraulic  laboratory  at  Fort  Collins, 
Colorado,  suggest  the  use  of  the  following  values  of  C  for  various 
size  of  openings.  If  these  values  are  used  the  per  cent  of  error  should 
be  less  than  6  per  cent,  unless  other  conditions  in  the  individual  struc- 
ture are  exceptionally  bad. 


CIRCULAR  250]  MEASUREMENT  OF  IRRIGATION  WATER  23 

Area  of  opening 
in  square  feet  Value  of  C 

0.25  to  0.50 80 

0.50  to  1.95 73 

1.95  to  3.00 68 

These  values  of  C  can  only  be  considered  as  trustworthy  when  the 
orifice  is  constructed  according  to  the  drawing  (Fig.  10).  Any  change 
in  the  size  of  the  posts  or  their  location  with  respect  to  the  flume  would 
doubtlessly  result  in  different  side  or  bottom  contractions.  Other 
factors  would  then  be  introduced  which  would  render  these  values  of 
C  unreliable. 

The  writer  would  be  glad  to  correspond  with  water  masters  and 
irrigation  managers  in  regard  to  the  experiments  mentioned  above. 


DESCBIPTION  OF  INCH  BOX  MEASUEEMENT 

A  miner's  inch  is  the  amount  of  water  which  will  flow  through 
an  opening  one  inch  square  when  the  center  of  that  opening  is  held 
under  a  definite  pressure.  This  required  pressure  varies  in  different 
localities.  In  most  of  the  western  states  this  pressure  is  fixed  by  the 
laws  of  the  states. 

In  California,  although  the  statute  specifies  a  pressure  of  six 
inches  above  the  center  of  the  opening,  a  pressure  of  four  inches  is 
in  universal  use  in  the  southern  part  of  the  state.  In  the  newer 
fruit-growing  areas  of  the  Sierra  Nevada  foothills  the  statute  pres- 
sure of  six  inches  is  in  common  use. 

This  definition  of  a  miner's  inch  makes  the  measurement  of  water 
in  this  unit  a  simple  matter.  Many  structures  have  been  designed 
for  such  measurements.  In  these  devices  an  adjustable  opening  is 
so  placed  that  its  center  is  exactly  as  many  inches  below  a  fixed 
overflow  as  the  law  or  local  custom  prescribes.  By  regulating  this 
adjustable  opening  the  water  above  the  opening  can  be  backed  up 
until  the  water  surface  stands  at  the  exact  level  of  the  overflow. 
The  average  pressure  on  the  opening  is  then  that  pressure  which  is 
required  by  the  local  custom,  and  each  square  inch  in  the  opening 
delivers  one  miner's  inch.  The  discharge  through  the  opening  in 
miner's  inches  can  then  be  determined  by  measuring  the  opening 
and  computing  its  area  in  square  inches.  The  number  of  square 
inches  in  the  opening  is  the  number  of  miner's  inches  in  the  stream. 


24 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


EIVEESIDE    BOX 

The  device  used  on  the  Riverside  Canal  in  southern  California 
is  shown  in  use  in  figure  11.  The  water  enters  through  the  bottom 
of  the  box  and  is  measured  out  through  an  adjustable  cast-iron  meas- 
uring plate  in  the  end.  The  opening  of  this  plate  is  five  inches  high 
and  by  moving  the  iron  slide  gates  it  can  be  varied  in  width  up  to 
fourteen  inches.  The  top  of  the  plate  is  four  inches  above  the  center 
of  the  opening.     This  four-inch  pressure  conforms  to  the  custom  in 


Fig.  11.     Photograph  of  Riverside  miner's  inch  box. 


southern  California.  Thus,  if  the  slides  are  set  so  as  to  hold  the 
water  surface  at  the  top  of  the  plate,  the  discharge  in  miner's  inches 
will  equal  the  area  of  the  opening  in  square  inches.  Marks  one  inch 
apart  are  made  on  the  plate  to  assist  in  measuring  the  width.  When 
the  water  has  passed  through  the  plate,  it  is  usually  dropped  into 
a  concrete  pipe  line  and  led  to  the  point  of  use.  Care  should  be 
taken  in  planning  the  installation  so  that  the  water  pouring  through 
the  plate  will  have  a  free  fall  into  the  basin  below. 

In  cases  where  the  Riverside  box  is  used  on  pipe  lines  operating 
under  considerable  pressure  it  is  often  necessary  that  the  measur- 
ing plate  be  installed  in  a  standpipe  several  feet  high.  In  such  in- 
stallations the  water  pouring  through  the  plate  drops  into  another 


Circular  250]  MEASUREMENT  OF  IRRIGATION  WATER  25 

pipe  high  enough  to  provide  the  necessary  pressure  for  the  remainder 
of  the  line.  The  cost  of  installing  a  Riverside  measuring  plate  in  a 
concrete  pipe  line,  in  which  the  water  is  carried  under  pressure, 
varies  so  greatly  that  cost  figures  can  not  be  given. 

The  Riverside  box  shown  in  figure  11  is  designed  for  delivery  of 
water  into  open  ditches  or  into  pipe  lines  which  require  no  initial 
head.  Such  an  installation  would  cost  about  $15.00.  The  plate  alone 
sells  for  $2.50. 


ANAHEIM  UNION  WATER  COMPANY  MEASURING  BOX 

The  measuring  box  of  the  Anaheim  Union  "Water  Company  is 
designed  so  that  a  definite  amount  of  water  can  be  diverted  from 
the  company's  canal  into  the  farmer's  lateral  or  pipe  line.  The  de- 
vice consists  of  a  by-pass  into  which  water  can  be  diverted  from 
the  main  canal,  an  adjustable  miner's  inch  plate,  and  an  overflow 
crest,  so  set  that  any  water  diverted  from  the  main  in  excess  of  the 
quantity  required  pours  back  into  the  company's  ditch.  The  meas- 
uring plate  is  placed  so  that  the  center  line  of  the  adjustable  open- 
ing is  exactly  four  inches  below  the  overflow.  The  inaccuracies  of 
the  device  lie  in  the  fact  that  the  contractions*  about  the  opening 
are  very  seldom  complete.  These  inaccuracies  are  all  in  favor  of  the 
water  user.  Figure  12  shows  the  measuring  box  of  the  Anaheim 
Union  Water  Company  in  use. 


*  When  a  stream  of  flowing  water  passes  over  a  weir  having  a  crest  length 
less  than  the  width  of  the  channel  in  which  the  water  is  flowing,  the  stream 
is  said  to  have  ' '  end  contractions. ' '  In  such  cases  the  actual  width  of  the  stream 
of  water  passing  over  the  weir  is  slightly  less  than  the  width  of  the  weir, 
this  being  due  to  the  curvature  of  the  water  around  the  sides  of  the  weir. 
Complete  end  contractions  for  any  given  weir  opening  are  reached  with  a 
maximum  curvature  of  the  wall  and  therefore  with  the  maximum  decrease 
in  the  width  of  the  stream.  Through  numerous  experiments  made  by  hydraulic 
engineers,  the  distance  the  sides  of  a  weir  must  be  from  the  sides  of  the 
channel  in  which  it  is  placed  in  order  to  give  complete  contractions  have  been 
determined  and  with  any  distance  less  than  this,  the  contractions  would  be 
il incomplete' y  and  the  quantity  of  water  actually  flowing  over  the  weir  will 
be  somewhat  different  from  that  shown  in  the  table  for  weirs  with  complete 
contractions.  A  weir  with  crest  length  equal  to  the  width  of  the  channel  in 
which  the  weir  is  placed  gives  no  end  contraction  or  narrowing  of  the  stream 
as  it  passes  over  the  weir.  Such  a  weir  is  known  as  a  "suppressed"  weir 
and  different  tables  must  be  used  with  it.  Such  tables  are  not  included  in 
this  circular  because  suppressed  weirs  are  seldom  used  by  farmers. 

The  term  "complete  contractions"  is  also  sometimes  used  in  connection 
with  weirs  to  denote  contractions  on  both  sides  and  bottom;  or  in  the  case 
of  an  orifice,  to  denote  contractions  on  all  four  sides. 


26 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


SANTA   ANA  VALLEY   IRKIGATTON   COMPANY'S   MINER'S   INCH   BOX 

A  somewhat  different  type  of  inch  box  is  used  by  the  Santa  Ana 
Valley  Irrigation  Company,  in  Orange  County.  This  is  merely  a 
cemented  section  of  the  lateral  in  which  the  measuring  board  is 
placed.  Water  is  forced  into  this  cemented  section  of  the  lateral  by 
stop  gates  placed  across  the  main  ditch.  The  farm  lateral  at  the 
point  of  measurement  is  uniformly  33%  inches  wide.     The  opening 


Fig.  12.     The  Anaheim  Union  Water  Company's  miner's  inch  box. 

is  three  inches  high.  If  a  stream  of  100  miner's  inches  is  desired, 
water  is  turned  into  the  lateral  until  it  stands  four  inches  above  the 
center  of  the  opening  in  the  measuring  plate.  If  only  fifty  miner's 
inches  are  required,  an  opening  one-half  the  width  of  the  box  is  used. 
This  opening  is  on  one  side  of  the  lateral,  however,  instead  of  in 
the  center,  giving  only  one  end  contraction  of  the  stream  of  water 
passing  through.  As  a  result  of  this,  and  also  because  there  is  no 
contraction  on  the  bottom  of  the  opening,  the  quantity  measured 
does  not  correspond  exactly  with  the  amount  measured  through  an 
opening  of  the  same  size,  with  contractions  on  all  four  sides. 

THE  AZUSA  HYDRANT 
It  will  be  noted  that  the  Riverside  box  described  above  can  be 
used  only  for  measuring  the  total  flow  in  a  ditch  or  pipe  line.     In 


Circular  250] 


MEASUREMENT  OF  IRRIGATION  WATER 


27 


cases  where  the  device  must  separate  a  certain  flow  from  a  larger 
stream  some  other  method  must  be  used.  A  common  device  of  this 
sort  is  the  Azusa  hydrant.     This  hydrant  is  used  exclusively  on  con- 


Fig.  13.     Drawing  of  Azusa  miner 's  inch  box. 


crete  pipe  lines  and  is  usually  used  to  separate  from  the  water  com- 
pany's supply  line  the  amount  of  water  ordered  by  individual  users. 
This  hydrant  (Figs.  13  and  14)  chiefly  provides  for  measure- 
ment through  one  or  more  orifices  on  the  center  of  which  a  pressure 
head  of  four  inches  is  maintained  by  means  of  a  sheet-iron  spill  crest 
set  at  right  angles  to  the  orifice  plate.  The  hydrant  is  in  the  form  of 
a  concrete  box  placed  over  the  supply  pipe  line.  The  openings  in 
the  orifice  plate  are  four  inches  high  and  2y2,  3%,  6%,  and  12% 


28 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


inches  wide,  giving  areas  of  10,  15,  25,  and  50  square  inches,  respec- 
tively. When  the  water  surface  on  the  upper  side  of  these  orifices 
is  held  four  inches  above  their  centers  they  will  discharge,  respec- 
tively, 10,  15,  25,  and  50  inches.  By  using  different  combinations  of 
these  orifices  several  different  amounts  up  to  100  inches  can  be  meas- 
ured.   The  water  enters  through  the  pipe  shown  in  the  drawing  (Fig. 


>    ,       3&V  ■  ' 


Fig.  14.     Photograph  of  Azusa  miner's  inch  box.     Taken  from  above. 

13).  The  orifices  for  the  desired  amounts  to  be  turned  out  are  opened 
and  the  others  closed  with  slides.  By  adjusting  the  gate  under  the 
spillway  the  water  can  be  brought  to  the  crest  of  the  spillway.  If 
the  water  rises  above  the  spillway  a  large  part  of  the  excess  will  be 
carried  back  to  the  supply  line  over  the  spillway,  but  any  increase 
in  depth  on  the  orifices  will  also  increase  the  amount  turned  out. 

The  Azusa  hydrant  as  shown  has  walls  six  inches  thick,  all  sides 
being  vertical.  The  forms  required  in  making  it  are  therefore  simple. 
The  box  contains  78.3  cubic  feet  of  concrete.     This  can  be  made  of 


Circular  250]  MEASUREMENT  OF  IRRIGATION  WATER  29 

one  part  cement  and  four  parts  coarse  sand.  As  the  walls  are  six 
inches  thick  it  is  better  to  add  some  gravel  (not  larger  than  iy2 
inches)  to  the  sand  where  this  can  be  obtained  cheaply,  but  the  pro- 
portion of  one  part  cement  to  four  parts  of  aggregate  should  be 
maintained.  The  concrete  for  this  box  including  forms  will  cost  from 
$18.00  to  $20.00  under  a  large  contract  and  about  $30.00  if  made 
singly.  The  plate  with  the  openings  and  slides  can  be  bought  already 
made  for  $12.50  from  foundries  in  the  vicinity  of  the  places  the 
hydrant  is  used.  The  gate  can  be  any  of  the  usual  types  of  slide  gate. 
The  average  of  a  number  of  tests  made  of  this  hydrant  at  Davis 
showed  the  amounts  in  inches  being  carried  through  the  openings 
to  be  one  per  cent  more  than  their  area  in  square  inches.  This  dif- 
ference includes  all  errors  in  the  measurements  so  that  these  openings 
are  seen  to  be  very  accurate.  The  tests  showed  all  openings  or  com- 
binations of  openings  to  be  equally  accurate.  The  box  will  there- 
fore measure  as  accurately  as  is  required.  The  openings  are  not  as 
closely  adjustable  to  the  amounts  turned  out,  however,  as  they  are 
in  the  case  of  the  box  of  the  Riverside  Water  Company.  Errors  to 
be  avoided  in  the  use  of  this  hydrant  result  from  allowing  the  water 
to  pass  through  the  openings  unevenly,  which  produces  a  swirling 
motion  of  the  water  as  it  rises  to  the  openings ;  also  from  not  so  ad- 
justing the  gate  under  the  spill-crest  as  to  keep  the  flow  over  the 
spill  to  a  thin  film  of  water. 

DIVISION  BOXES 

In  some  places  in  California,  as  well  as  in  other  western  states, 
the  waters  in  small  streams  are  so  allotted  that  an  individual  user  is 
entitled  to  a  definite  proportion  of  the  entire  flow  of  that  stream.  This 
proportion  is  usually  fixed  by  consideration  of  the  number  of  irri- 
gable acres  each  owner  farms  and  the  age  of  the  established  water 
rights.  Canal  companies  in  areas  where  this  method  of  proportional 
delivery  is  common  have  at  times  adopted  division  boxes  for  the  divi- 
sion and  distribution  of  their  supply.  In  such  cases  the  company  is 
commonly  organized  as  a  stock  company  and  the  stock  purchased 
by  the  water  users.  One  share  of  stock  usually  represents  one  acre 
of  irrigable  land.  If,  for  instance,  100  shares  of  stock  have  been 
sold  in  a  ditch  company  and  one  user  owns  ten  shares,  that  user  is 
entitled  to  10/100  of  the  entire  flow  of  the  canal.  Many  types  of 
division  boxes  have  been  designed  in  an  effort  to  make  this  propor- 
tionate division  just  and  accurate.  All  of  these  devices  are  based 
upon  the  principle  that  for  a  given  head  the  discharge  over  two  weir 


30  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

crests  set  at  the  same  elevation  is  approximately  proportional  to  the 
length  of  those  weir  crests. 

In  the  example  given  above  the  water  user  is  entitled  to  10/100 
of  all  the  water  in  the  canal.  Such  a  division  might  be  made  by  set- 
ting two  weirs  at  the  same  elevation  in  the  canal  near  the  farmer's 
turnout.  If,  for  example,  one  of  the  weirs  has  a  crest  ten  inches 
long  and  discharges  its  water  into  the  farmer's  lateral,  and  the  other 
weir  with  a  crest  ninety  inches  long  empties  its  water  into  the  com- 
pany's ditch,  this  proportionate  division  would  be  equitably  accom- 
plished, since  the  lengths  of  the  weir  crests  would  have  the  same 
ratio  as  that  required  by  the  conditions  of  the  diversion.  No  matter 
how  much  water  came  down  the  canal,  the  user  would  receive  10/100 
of  the  entire  flow. 

These  division  weirs  are  subject  to  the  conditions  already  given 
for  other  weirs.  These  conditions  are  usually  difficult  to  obtain 
throughout  the  length  of  a  canal.  The  users  at  the  upper  end  of 
the  canal  do  not  contribute  toward  the  payment  for  water  lost  by 
seepage  below  them  in  the  canal  and  the  whole  charge  for  this  loss 
falls  on  the  users  at  the  lower  end. 

Several  structures  have  been  designed  to  obviate  these  difficul- 
ties, but  in  most  cases  this  has  been  done  at  the  sacrifice  of  accuracy 
in  the  division. 

An  isometric  drawing  of  one  of  these  devices  is  shown  in  figure 
15.  With  this  structure  the  water  enters  the  flume  at  the  left,  is 
divided  into  the  required  proportion  by  the  vertical  cutwater,  and 
is  discharged  into  the  user's  flume  which  leads  off  to  the  right  or 
runs  out  of  the  flume  and  into  the  company's  ditch  again.  A  flat 
crested  weir  set  across  both  divisions  of  the  flume  and  about  three 
feet  back  from  the  entering  end  aids  in  the  just  division.  In  a  struc- 
ture of  this  sort  the  dividing  partition  in  the  flume  is  so  set  that  its 
distance  from  the  water  user's  side  of  the  box  holds  the  same  propor- 
tion to  the  whole  width  as  the  number  of  shares  of  stock  owned  by 
the  water  user  holds  to  the  number  of  shares  below  him  plus  those 
he  holds  himself.  In  the  case  as  given  above  the  user  owned  ten 
shares  of  stock.  One  hundred  shares  had  to  be  served  by  the  water 
in  the  canal.  The  partition  in  his  box  would  then  be  built  so  that 
it  stood  10/100  of  the  way  across  the  box.  He,  of  course,  would  re- 
ceive the  water  pouring  through  the  narrower  compartment.  The 
hinged  gate  at  the  beginning  of  the  user's  flume  will  allow  him  to 
turn  water  into  his  ditch  or  back  into  the  company's  canal  at  will. 

Such  a  structure  assumes  that  water  flows  with  an  equal  velocity 
at  all  points  in  a  stream.  This  is  never  or  very  seldom  the  case,  for 
the  water  near  the  banks  is  necessarily  slowed  down  by  weeds,  rocks 


Circular  250] 


MEASUREMENT  OF  IRRIGATION  WATER 


31 


or  irregular  earth  work  of  the  banks  and  bottom.  With  such  a  box 
the  water  user  will  usually  receive  less  water  than  he  is  entitled  to, 
for  his  share  is  taken  from  an  area  of  reduced  velocity  while  the 
water  running  past  him  comes  from  the  fastest-flowing  part  of  the 
stream. 

A  box  such  as  that  described  above  contains  about  650  board  feet 
of  lumber. 


Note: Gate  to  bo 
'at  this 
■post 
U**3'6' 


Fig.  15.  Drawing  of  proportional  division  box. 
MECHANICAL.  DEVICES  FOR  MEASURING  WATER  VOLUMETRICALLY 
It  frequently  is  desirable  that  a  measuring  device  should  record 
the  volume  of  water  delivered  to  irrigators,  rather  than  the  rate  of 
flow.  Numerous  mechanically  recording  devices  have  been  designed 
to  accomplish  this,  several  of  these  being  described  below.  Without 
discussing  the  individual  merits  of  these  devices,  it  may  be  said  that 
although  several  of  them  are  in  use  in  California  and  are  believed  by 
those  using  them  to  be  giving  more  or  less  satisfactory  service,  there 
are  many  practical  difficulties  involved  in  operating  devices  of  this 
nature.  It  would,  therefore,  seem  that  when  a  mechanical  device  is 
selected  for  measuring  individual  farmer's  deliveries  of  irrigation 
water,  the  practical  limitations  of  the  device  chosen  should  be  under- 
stood. This  is  desirable  in  order  that  care  may  be  taken  to  provide 
the  conditions  necessary  for  satisfactory  measurements,  and  also  that 
the  need  for  occasional  tests  of  the  operating  accuracy  of  the  devices 
may  be  appreciated. 


32 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


EELIANCE  METER 

The  Reliance  meter  consists  of  a  brass  vane,  shaped  something 
like  a  propeller  wheel,  set  in  a  throat,  and  a  brass  rod  which  connects 
the  vane  to  the  recording  head.  This  recording  head  contains  gear- 
ing which  is  connected  with  a  counter.  The  figures  in  this  counter 
show  the  number  of  acre-feet  of  water  which  have  passed  through 
the  device. 


Fig.  16.     Photograph  of  Reliance  meter. 


This  apparatus  is  set  so  that  the  water  to  be  measured  pours  be- 
tween a  series  of  plates  or  vanes  and  on  to  the  propeller  shaft  in  the 
throat.    It  can  be  used  in  either  open  ditches  or  concrete  pipe  lines. 

The  great  advantage  of  such  a  device  lies  in  the  fact  that  it  shows 
at  a  glance  how  many  acre-feet  of  water  have  passed  through  the 
meter.  With  most  other  devices  some  computations  are  necessary  to 
change  the  expression  of  the  flow  in  cubic  feet  per  second  into  terms 
of  acre-feet. 

Figure  16  is  a  photograph  of  a  Reliance  meter  installed  on  a  con- 
crete pipe  line. 


Circular  250] 


MEASUREMENT  OF  IRRIGATION  WATER 


33 


DETHRIDGE   METER 

In  the  Keliance  meter  only  a  part  of  the  stream  hits  the  propeller 
wheel  and  turns  it.  In  the  Dethridge  meter  (Fig.  17)  the  whole 
flow  of  the  stream  is  directed  against  the  wheel.  The  wheel  in  this 
case  is  a  large  sheet-iron  drum,  three  feet,  four  inches  in  diameter 
and  two  feet,  six  inches  wide.  Attached  to  the  outer  surface  of  this 
drum  are  a  series  of  heavy  blades  which  extend  ten  inches  beyond 
the  circumference  of  the  drum. 


Fig.  17.     Photograph  of  Dethridge  meter. 

This  drum  turns  in  hardwood  bearings  attached  to  the  concrete 
base.  When  the  wheel  turns  the  projecting  blades  fit  closely  into  a 
depression  in  the  concrete  floor  of  the  device. 

Water,  when  turned  into  the  device,  presses  successively  against 
the  blades  on  the  cylinder  and  turns  it  in  the  bearings.  A  counter 
can  easily  be  arranged  to  record  these  revolutions.  With  a  Dethridge 
meter  of  the  size  described  above,  the  discharge  per  revolution  is 
about  30.5  cubic  feet  of  water,  regardless  of  the  speed  at  which  the 
wheel  revolves.  Each  wheel  installed  should  be  accurately  calibrated 
to  determine  the   quantity  of  water   discharged  by   the  wheel   per 


34  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

revolution.  The  Dethridge  meter  has  been  very  popular  in  Australia 
where  a  large  number  are  in  use.  The  device  has  never  been  used 
for  the  practical  measurement  of  water  in  California.  A  description 
of  the  Dethridge  meter  is  included  in  this  circular  because  it  involves 
a  new  principle. 


OTHER  MEASURING  DEVICES 

The  Lyman  meter.  Many  mechanical  devices  have  been  invented 
and  patented  by  which  the  flow  over  weirs  can  be  read  as  a  quantity 
in  terms  of  acre-feet,  in  place  of  as  a  rate  of  flow  as  in  cubic  feet 
per  second.  One  of  the  more  recent  of  these  devices  is  the  Lyman 
meter. 

The  Lyman  meter  consists  of  a  small,  delicately  balanced  brass 
turbine  wheel,  enclosed  in  a  brass  shell.  This  shell  is  attached  to 
the  down-stream  face  of  a  weir  bulkhead  and  must  be  so  set  that  a 
hole  bored  through  the  weir  bulkhead  and  leading  into  the  turbine 
shell  shall  have  a  fixed  relation  with  the  weir  notch.  On  the  up- 
stream side  of  the  weir  board  is  a  brass  tube  in  which  carefully  placed 
openings  have  been  cut.  This  brass  tube  connects  at  its  base  with 
a  short  length  of  pipe  which  passes  through  the  weir  bulkhead  and 
into  the  turbine  shell. 

The  holes  in  the  brass  tube  on  the  up-stream  side  of  the  weir 
bulkhead  are  of  such  varying  diameters  that  they  separate  a  cer- 
tain definite  proportion  of  the  water  from  the  stream  going  over  the 
weir,  no  matter  at  what  height  the  water  may  stand  above  the  weir. 
This  small  flow  passes  down  the  tube,  through  the  bulkhead  and  into 
the  turbine  shell,  where  it  revolves  the  small  turbine  wheel.  This 
wheel  is  geared  to  a  counter  in  such  a  way  that  the  quantity  can 
be  read  directly  on  the  face  of  the  counter. 

Different  sizes  of  turbine  wheels  and  different  calibrations  on 
the  up-stream  tube  are  necessary  for  use  with  weirs  of  various  types 
and  various  lengths  of  crest. 

The  Sentinel  meter.  This  meter  is  mounted  in  a  2-foot  section  of 
steel  pipe  designed  to  be  set  in  an  irrigation  pipe  line,  the  size  of  the 
meter  and  of  the  steel  section  depending  on  the  size  of  such  pipe  line. 
A  wheel  or  turbine  set  in  the  steel  section  turns  as  the  water  passes 
through  the  pipe  line,  the  revolutions  of  the  wheel  being  indicated  by 
a  counter  set  in  a  dial  above  the  steel  section,  the  gearing  being  so 
arranged  that  the  quantity  of  water  passing  is  directly  indicated  by 
the  counter. 


CIRCULAR  250]  MEASUREMENT  OF  IRRIGATION  WATER  35 

The  Vcnturi  meter.  The  Venturi  meter  is  a  device  for  the  ac- 
curate measurement  of  relatively  large  flows  of  water.  This  device, 
in  irrigation  systems,  is  confined  to  large  diversions  from  main  canals 
into  laterals  and  not  to  the  measurement  of  water  from  the  lateral 
to  the  individual  user. 

The  Venturi  flame.  The  Venturi  flume  is  similar  to  the  Venturi 
meter  in  theory.  "Water  in  an  open  ditch  is  led  into  a  structure 
through  a  narrow  throat  and  out  into  the  original  channel.  In  pass- 
ing through  this  constricted  cross-section,  a  difference  in  head  above 
the  device  and  in  the  throat  always  results.  This  difference  in  head, 
which  may  be  determined  as  in  the  submerged  orifice,  is  the  measure 
of  the  amount  of  water  which  passes  through  the  device.  Tables 
and  curves  have  been  prepared  to  aid  in  determining  the  amount  of 
water  passing  through  the  Venturi  flume  when  the  difference  iu 
water  level  above  and  below  the  device  is  known.  The  difference 
in  head  which  results  when  a  stream  of  water  passes  through  the 
Venturi  flume  may  be  so  small  that  it  is  very  difficult  to  measure  it 
accurately. 

SUMMAEY 

Common  devices  for  measuring  irrigation  water  in  California  in- 
clude rectangular,  Cipolletti,  and  triangular  weirs,  submerged  ori- 
fices with  fixed  and  with  adjustable  openings,  various  miner 's-inch 
boxes  and  hydrants,  and  numerous  mechanical  devices  for  registering 
the  volume  of  water  that  passes  through  them. 

In  cases  where  the  water  to  be  measured  is  free  from  silt  and 
where  the  grade  of  the  ditch  is  sufficient  to  allow  for  the  required 
backing  up  of  the  stream,  some  type  of  weir  is  undoubtedly  the  most 
satisfactory  device. 

A  weir  is  accurate,  cheap,  easily  installed  and  has  no  moving 
parts  to  get  out  of  order.  For  small  heads  of  water,  a  triangular  or 
"V"  notch  weir  is  most  accurate.  For  larger  heads  a  rectangular 
weir  is  most  satisfactory.  A  Cipolletti  weir  seems  to  have  no  ad- 
vantage over  a  rectangular  weir;  it  is  harder  to  construct  and  for 
this  reason  is  liable  to  be  more  inaccurate  than  the  simple  rectangular 
weir. 

If  the  ditch  grade  at  the  required  point  of  measurement  is  so 
flat  that  the  necessary  fall  over  a  weir  crest  can  not  be  provided,  or 
if  the  water  to  be  measured  is  so  heavily  charged  with  silt  that  a 
weir  pond  would  rapidly  fill  up,  a  submerged  orifice  may  be  con- 
sidered the  most  satisfactory  device. 


36  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

A  submerged  orifice  of  fixed  dimensions,  if  carefully  installed  and 
with  careful  measurements  for  the  difference  in  head,  will  give  fairly 
accurate  results.  Accuracy  is  necessarily  sacrificed  when  wide  fluc- 
tuations in  the  stream  to  be  measured  make  it  necessary  to  install 
an  adjustable  orifice.  With  the  adjustable  orifice  the  coefficient 
"C,M  which  is  used  in  determining  the  discharge,  varies  with  the 
area  of  the  opening.  Besides  this  indefinite  value  of  "C"  there  is  an 
added  complication  due  to  variation  in  individual  boxes.  The  skill  of 
the  carpenter  who  builds  the  device  may  affect  its  discharge  to  a  con- 
siderable extent  under  given  conditions.  At  times  an  adjustable  sub- 
merged orifice  is  the  only  device  at  all  suited  to  the  conditions  which 
must  be  met. 

Miner 's  inch  boxes  are  used  chiefly  in  the  foothill  orchard  sec- 
tions and  in  the  citrus  sections  of  southern  California.  These  are 
usually  installed  by  the  company  furnishing  the  water.  If  carefully 
installed  and  proper  conditions  of  measurement  are  maintained,  they 
will  give  approximately  correct  results. 


